<s>
Duolingo	B-Application
(	O
)	O
is	O
an	O
American	O
educational	O
technology	O
company	O
which	O
produces	O
learning	O
apps	B-Application
and	O
provides	O
language	O
certification	O
.	O
</s>
<s>
The	O
platform	O
was	O
founded	O
in	O
2011	O
by	O
Luis	O
von	O
Ahn	O
and	O
Severin	O
Hacker	O
and	O
has	O
since	O
grown	O
to	O
become	O
one	O
of	O
the	O
most	O
popular	O
language	O
learning	O
apps	B-Application
in	O
the	O
world	O
.	O
</s>
<s>
Duolingo	B-Application
offers	O
a	O
wide	O
range	O
of	O
language	O
courses	O
,	O
teaching	O
over	O
100	O
languages	O
,	O
from	O
popular	O
languages	O
such	O
as	O
English	O
,	O
Spanish	O
,	O
French	O
,	O
and	O
German	O
,	O
to	O
less	O
commonly	O
studied	O
languages	O
such	O
as	O
Welsh	O
,	O
Irish	O
,	O
and	O
Swahili	O
.	O
</s>
<s>
Duolingo	B-Application
also	O
offers	O
the	O
Duolingo	B-Application
English	O
Test	O
certification	O
program	O
and	O
a	O
literacy	O
app	O
for	O
children	O
called	O
Duolingo	B-Application
ABC	O
,	O
and	O
the	O
company	O
released	O
an	O
elementary	O
level	O
math	O
app	O
called	O
Duolingo	B-Application
Math	O
currently	O
exclusive	O
to	O
iOS	B-Application
.	O
</s>
<s>
Duolingo	B-Application
offers	O
a	O
premium	O
service	O
which	O
eliminates	O
advertising	O
and	O
offers	O
more	O
features	O
.	O
</s>
<s>
The	O
idea	O
for	O
Duolingo	B-Application
was	O
initiated	O
at	O
the	O
end	O
of	O
2009	O
in	O
Pittsburgh	O
by	O
Carnegie	O
Mellon	O
University	O
professor	O
Luis	O
von	O
Ahn	O
and	O
his	O
Swiss-born	O
post-graduate	O
student	O
Severin	O
Hacker	O
.	O
</s>
<s>
Hacker	O
(	O
co-founder	O
and	O
current	O
CTO	O
of	O
Duolingo	B-Application
)	O
believed	O
that	O
"	O
free	O
education	O
will	O
really	O
change	O
the	O
world	O
"	O
and	O
wanted	O
to	O
supply	O
people	O
an	O
outlet	O
to	O
do	O
so	O
.	O
</s>
<s>
The	O
founders	O
considered	O
creating	O
Duolingo	B-Application
as	O
a	O
nonprofit	O
organization	O
but	O
Von	O
Ahn	O
judged	O
this	O
model	O
as	O
unsustainable	O
.	O
</s>
<s>
This	O
was	O
replaced	O
as	O
a	O
source	O
of	O
revenue	O
by	O
a	O
Duolingo	B-Application
English	O
Test	O
certification	O
program	O
,	O
advertising	O
and	O
subscription	O
.	O
</s>
<s>
In	O
October	O
2011	O
,	O
Duolingo	B-Application
announced	O
that	O
it	O
had	O
raised	O
$3.3	O
million	O
from	O
a	O
Series	O
A	O
round	O
of	O
funding	O
,	O
led	O
by	O
Union	O
Square	O
Ventures	O
,	O
with	O
participation	O
from	O
author	O
Tim	O
Ferriss	O
and	O
actor	O
Ashton	O
Kutcher	O
's	O
investing	O
firm	O
A-Grade	O
Investments	O
.	O
</s>
<s>
Duolingo	B-Application
launched	O
a	O
private	O
beta	O
on	O
November	O
27	O
,	O
2011	O
,	O
and	O
accumulated	O
a	O
waiting	O
list	O
of	O
more	O
than	O
300,000	O
people	O
.	O
</s>
<s>
In	O
September	O
2012	O
,	O
Duolingo	B-Application
announced	O
that	O
it	O
had	O
raised	O
a	O
further	O
$15	O
million	O
from	O
a	O
Series	O
B	O
funding	O
round	O
led	O
by	O
New	O
Enterprise	O
Associates	O
,	O
with	O
participation	O
from	O
Union	O
Square	O
Ventures	O
.	O
</s>
<s>
In	O
November	O
2012	O
,	O
Duolingo	B-Application
released	O
an	O
iPhone	B-Device
app	O
,	O
followed	O
an	O
Android	B-Application
app	O
in	O
May	O
2013	O
,	O
at	O
which	O
time	O
Duolingo	B-Application
had	O
a	O
user	O
base	O
of	O
around	O
3	O
million	O
.	O
</s>
<s>
By	O
July	O
2013	O
,	O
the	O
service	O
had	O
grown	O
to	O
5	O
million	O
users	O
and	O
was	O
rated	O
the	O
#1	O
free	O
education	O
app	O
in	O
the	O
Google	B-Application
Play	I-Application
store	I-Application
.	O
</s>
<s>
In	O
February	O
2014	O
,	O
Duolingo	B-Application
announced	O
that	O
it	O
had	O
raised	O
$20	O
million	O
from	O
a	O
Series	O
C	O
funding	O
round	O
led	O
by	O
Kleiner	O
Caufield	O
&	O
Byers	O
,	O
with	O
prior	O
investors	O
also	O
participating	O
.	O
</s>
<s>
At	O
this	O
time	O
,	O
Duolingo	B-Application
had	O
34	O
employees	O
and	O
reported	O
having	O
about	O
25	O
million	O
registered	O
users	O
and	O
12.5	O
million	O
active	O
users	O
,	O
though	O
it	O
later	O
reported	O
a	O
figure	O
closer	O
to	O
60	O
million	O
users	O
.	O
</s>
<s>
In	O
June	O
2015	O
,	O
Duolingo	B-Application
announced	O
that	O
it	O
had	O
raised	O
$45	O
million	O
from	O
a	O
Series	O
D	O
funding	O
round	O
led	O
by	O
Google	O
Capital	O
,	O
bringing	O
its	O
total	O
funding	O
to	O
$83.3	O
million	O
.	O
</s>
<s>
In	O
April	O
2016	O
,	O
it	O
was	O
reported	O
that	O
Duolingo	B-Application
had	O
more	O
than	O
18	O
million	O
monthly	O
users	O
.	O
</s>
<s>
In	O
July	O
2017	O
,	O
Duolingo	B-Application
announced	O
that	O
it	O
had	O
raised	O
$25	O
million	O
in	O
a	O
Series	O
E	O
funding	O
round	O
led	O
by	O
Drive	O
Capital	O
,	O
bringing	O
its	O
total	O
funding	O
to	O
$108.3	O
million	O
.	O
</s>
<s>
The	O
round	O
valued	O
Duolingo	B-Application
at	O
$700	O
million	O
,	O
and	O
the	O
company	O
reported	O
passing	O
200	O
million	O
registered	O
users	O
,	O
with	O
25	O
million	O
active	O
users	O
.	O
</s>
<s>
It	O
was	O
reported	O
that	O
Duolingo	B-Application
had	O
95	O
employees	O
.	O
</s>
<s>
On	O
August	O
1	O
,	O
2018	O
,	O
Duolingo	B-Application
surpassed	O
300	O
million	O
registered	O
users	O
.	O
</s>
<s>
In	O
December	O
2019	O
,	O
it	O
was	O
announced	O
that	O
Duolingo	B-Application
raised	O
$30	O
million	O
in	O
a	O
Series	O
F	O
funding	O
round	O
from	O
Alphabet	O
's	O
investment	O
company	O
CapitalG	O
.	O
</s>
<s>
The	O
round	O
valued	O
Duolingo	B-Application
at	O
$1.5	O
billion	O
.	O
</s>
<s>
Duolingo	B-Application
reported	O
30	O
million	O
active	O
users	O
at	O
this	O
time	O
.	O
</s>
<s>
Duolingo	B-Application
planned	O
to	O
use	O
the	O
funds	O
to	O
develop	O
new	O
products	O
and	O
further	O
expand	O
its	O
team	O
in	O
sectors	O
like	O
engineering	O
,	O
business	O
development	O
,	O
design	O
,	O
curriculum	O
and	O
content	O
creators	O
,	O
community	O
outreach	O
,	O
and	O
marketing	O
.	O
</s>
<s>
In	O
October	O
2013	O
,	O
Duolingo	B-Application
launched	O
a	O
crowdsourced	O
language	O
incubator	O
.	O
</s>
<s>
In	O
March	O
2021	O
,	O
Duolingo	B-Application
announced	O
that	O
it	O
will	O
be	O
ending	O
its	O
volunteer	O
contributor	O
program	O
and	O
donating	O
money	O
to	O
its	O
volunteer	O
contributors	O
who	O
helped	O
to	O
make	O
Duolingo	B-Application
.	O
</s>
<s>
On	O
28	O
June	O
2021	O
,	O
Duolingo	B-Application
filed	O
for	O
an	O
initial	O
public	O
offering	O
on	O
NASDAQ	O
under	O
the	O
ticker	O
DUOL	O
.	O
</s>
<s>
From	O
August	O
2021	O
to	O
June	O
2022	O
,	O
the	O
Duolingo	B-Application
language	O
learning	O
app	O
was	O
removed	O
from	O
some	O
app	O
stores	O
in	O
China	O
.	O
</s>
<s>
In	O
the	O
early	O
2020s	O
,	O
Duolingo	B-Application
was	O
noted	O
for	O
their	O
viral	O
videos	O
on	O
the	O
social	O
media	O
platform	O
TikTok	B-Application
.	O
</s>
<s>
In	O
August	O
2022	O
,	O
Duolingo	B-Application
overhauled	O
its	O
user	O
interface	O
and	O
user	O
experience	O
,	O
changing	O
the	O
structure	O
of	O
the	O
courses	O
from	O
a	O
tree-like	O
design	O
where	O
users	O
could	O
choose	O
from	O
a	O
range	O
of	O
lessons	O
after	O
completing	O
previous	O
ones	O
,	O
to	O
a	O
linear	O
progression	O
.	O
</s>
<s>
CEO	O
Luis	O
von	O
Ahn	O
said	O
that	O
they	O
had	O
no	O
plans	O
of	O
undoing	O
the	O
changes	O
,	O
commenting	O
that	O
their	O
decision	O
was	O
made	O
in	O
order	O
to	O
simplify	O
Duolingo	B-Application
for	O
new	O
users	O
,	O
and	O
that	O
maintaining	O
both	O
the	O
old	O
and	O
new	O
versions	O
would	O
be	O
difficult	O
.	O
</s>
<s>
In	O
October	O
2022	O
,	O
Duolingo	B-Application
acquired	O
Detroit-based	O
animation	O
studio	O
Gunner	O
.	O
</s>
<s>
Duolingo	B-Application
uses	O
a	O
gamified	O
approach	O
to	O
language	O
learning	O
,	O
with	O
lessons	O
that	O
incorporate	O
translating	O
,	O
interactive	O
exercises	O
,	O
quizzes	O
,	O
and	O
stories	O
to	O
make	O
learning	O
more	O
engaging	O
and	O
fun	O
.	O
</s>
<s>
For	O
some	O
languages	O
Duolingo	B-Application
offers	O
podcasts	B-Operating_System
for	O
people	O
in	O
intermediate	O
level	O
consisting	O
on	O
stories	O
told	O
usually	O
by	O
native	O
speakers	O
from	O
different	O
parts	O
of	O
the	O
world	O
where	O
the	O
target	O
language	O
is	O
spoken	O
,	O
but	O
with	O
simplified	O
grammar	O
,	O
vocabulary	O
,	O
and	O
with	O
a	O
slower	O
intonation	O
,	O
as	O
well	O
with	O
occasional	O
assistance	O
with	O
providing	O
context	O
or	O
explanations	O
of	O
unusual	O
words	O
in	O
the	O
source	O
language	O
by	O
a	O
narrator	O
.	O
</s>
<s>
Duolingo	B-Application
also	O
provides	O
a	O
competitive	O
space	O
.	O
</s>
<s>
Badges	O
in	O
Duolingo	B-Application
represent	O
achievements	O
that	O
are	O
earned	O
from	O
completing	O
specific	O
objectives	O
or	O
challenges	O
.	O
</s>
<s>
Duolingo	B-Application
provides	O
features	O
designed	O
to	O
allow	O
teachers	O
to	O
track	O
students	O
 '	O
progress	O
in	O
language	O
acquisition	O
.	O
</s>
<s>
Most	O
language-learning	O
features	O
in	O
Duolingo	B-Application
are	O
free	O
of	O
charge	O
,	O
but	O
it	O
has	O
periodic	O
advertising	O
in	O
both	O
its	O
mobile	O
and	O
web	B-Application
browser	I-Application
applications	O
,	O
which	O
users	O
can	O
remove	O
by	O
paying	O
a	O
subscription	O
fee	O
or	O
promoting	O
referral	O
links	O
.	O
</s>
<s>
This	O
feature	O
is	O
known	O
as	O
"	O
Super	O
Duolingo	B-Application
"	O
and	O
includes	O
benefits	O
such	O
as	O
unlimited	O
hearts	O
(	O
retries	O
)	O
,	O
level	O
skipping	O
,	O
no	O
ads	O
,	O
and	O
progress	O
quizzes	O
.	O
</s>
<s>
Duolingo	B-Application
offers	O
courses	O
in	O
the	O
following	O
languages	O
:	O
</s>
<s>
Duolingo	B-Application
ABC	O
is	O
a	O
mobile	B-Application
app	I-Application
for	O
young	O
children	O
for	O
learning	O
letters	O
,	O
their	O
sounds	O
,	O
phonics	O
,	O
and	O
other	O
foundational	O
early	O
reading	O
concepts	O
that	O
was	O
released	O
in	O
2020	O
.	O
</s>
<s>
Duolingo	B-Application
ABC	O
is	O
free	O
to	O
use	O
,	O
and	O
it	O
does	O
not	O
contain	O
any	O
ads	O
or	O
in-app	O
purchases	O
.	O
</s>
<s>
The	O
app	O
is	O
available	O
on	O
iOS	B-Application
and	O
Android	B-Application
devices	O
,	O
and	O
is	O
currently	O
offered	O
in	O
English	O
.	O
</s>
<s>
Duolingo	B-Application
Math	O
is	O
a	O
mobile	B-Application
app	I-Application
for	O
learning	O
elementary	O
mathematics	O
in	O
a	O
form	O
similar	O
to	O
the	O
original	O
app	O
,	O
released	O
in	O
October	O
2022	O
.	O
</s>
<s>
It	O
is	O
currently	O
only	O
available	O
on	O
iOS	B-Application
devices	O
.	O
</s>
<s>
Duolingo	B-Application
English	O
Test	O
(	O
DET	O
)	O
is	O
an	O
online	O
English	O
proficiency	O
test	O
that	O
measures	O
a	O
person	O
's	O
ability	O
to	O
communicate	O
in	O
English	O
.	O
</s>
<s>
The	O
Duolingo	B-Application
English	O
Test	O
is	O
entirely	O
computer-based	O
and	O
can	O
be	O
taken	O
from	O
any	O
location	O
with	O
an	O
internet	O
connection	O
.	O
</s>
<s>
One	O
of	O
the	O
main	O
advantages	O
of	O
the	O
Duolingo	B-Application
English	O
Test	O
is	O
its	O
convenience	O
and	O
accessibility	O
.	O
</s>
<s>
The	O
Duolingo	B-Application
English	O
Test	O
is	O
recognized	O
by	O
many	O
universities	O
,	O
colleges	O
,	O
and	O
other	O
organizations	O
as	O
an	O
alternative	O
to	O
other	O
English	O
proficiency	O
tests	O
.	O
</s>
<s>
Duolingo	B-Application
had	O
a	O
revenue	O
of	O
$1	O
million	O
in	O
2016	O
,	O
$13	O
million	O
in	O
2017	O
,	O
$36	O
million	O
in	O
2018	O
,	O
and	O
$250.77	O
million	O
in	O
2021	O
.	O
</s>
<s>
In	O
May	O
2022	O
,	O
it	O
was	O
reported	O
that	O
6.8	O
%	O
of	O
Duolingo	B-Application
's	O
monthly	O
active	O
users	O
pay	O
for	O
the	O
ad-free	O
version	O
of	O
the	O
app	O
.	O
</s>
<s>
Duolingo	B-Application
derived	O
most	O
of	O
its	O
revenue	O
from	O
subscription	O
,	O
advertising	O
,	O
and	O
its	O
Duolingo	B-Application
English	O
Test	O
.	O
</s>
<s>
In	O
April	O
2020	O
,	O
Duolingo	B-Application
passed	O
one	O
million	O
paid	O
subscribers	O
.	O
</s>
<s>
A	O
2017	O
study	O
found	O
no	O
significant	O
difference	O
between	O
elementary	O
students	O
learning	O
Spanish	O
through	O
the	O
"	O
gamification	O
"	O
of	O
Duolingo	B-Application
and	O
those	O
learning	O
in	O
classroom	O
environments	O
,	O
with	O
both	O
groups	O
demonstrating	O
a	O
similar	O
increase	O
in	O
achievements	O
and	O
self-efficacy	O
.	O
</s>
<s>
A	O
2022	O
study	O
on	O
adults	O
using	O
Duolingo	B-Application
as	O
their	O
only	O
language	O
learning	O
tool	O
,	O
published	O
in	O
the	O
journal	O
Foreign	O
Language	O
Annals	O
,	O
found	O
that	O
the	O
participants	O
that	O
completed	O
a	O
course	O
had	O
similar	O
proficiency	O
to	O
university	O
students	O
after	O
four	O
semesters	O
of	O
study	O
.	O
</s>
<s>
The	O
authors	O
therefore	O
suggested	O
that	O
Duolingo	B-Application
could	O
be	O
an	O
effective	O
tool	O
for	O
foreign	O
language	O
learning	O
.	O
</s>
<s>
Linguist	O
Steven	O
Sacco	O
at	O
San	O
Diego	O
State	O
University	O
attempted	O
to	O
test	O
Duolingo	B-Application
's	O
claim	O
that	O
"	O
34	O
hours	O
of	O
Duolingo	B-Application
are	O
equivalent	O
to	O
a	O
full	O
university	O
semester	O
of	O
language	O
education	O
"	O
by	O
completing	O
a	O
course	O
in	O
Swedish	O
,	O
and	O
taking	O
a	O
standardized	O
elementary	O
exam	O
,	O
ultimately	O
receiving	O
a	O
failing	O
grade	O
.	O
</s>
<s>
Sacco	O
suggested	O
that	O
Duolingo	B-Application
is	O
helpful	O
for	O
learning	O
vocabulary	O
only	O
in	O
addition	O
to	O
immersion	O
environments	O
like	O
a	O
classroom	O
.	O
</s>
<s>
In	O
2013	O
,	O
Apple	O
chose	O
Duolingo	B-Application
as	O
its	O
iPhone	B-Device
App	O
of	O
the	O
Year	O
,	O
the	O
first	O
time	O
this	O
honor	O
had	O
been	O
awarded	O
to	O
an	O
educational	O
application	O
.	O
</s>
<s>
In	O
2013	O
,	O
Duolingo	B-Application
ranked	O
on	O
Fast	O
Company	O
's	O
"	O
The	O
World	O
's	O
Most	O
Innovative	O
Companies	O
:	O
Education	O
Honorees	O
"	O
list	O
"	O
for	O
crowdsourcing	O
web	O
translation	O
by	O
turning	O
it	O
into	O
a	O
free	O
language-learning	O
program	O
"	O
.	O
</s>
<s>
Duolingo	B-Application
won	O
Best	O
Education	O
Startup	O
at	O
the	O
2014	O
Crunchies	O
,	O
and	O
was	O
the	O
most	O
downloaded	O
app	O
in	O
the	O
Education	O
category	O
in	O
Google	B-Application
Play	I-Application
in	O
2013	O
and	O
2014	O
.	O
</s>
<s>
In	O
2015	O
,	O
Duolingo	B-Application
was	O
announced	O
the	O
2015	O
award	O
winner	O
in	O
Play	O
&	O
Learning	O
category	O
by	O
Design	O
to	O
Improve	O
Life	O
.	O
</s>
<s>
Duolingo	B-Application
won	O
Inc	O
.	O
magazine	O
's	O
Best	O
Workplaces	O
2018	O
,	O
Entrepreneur	O
magazine	O
's	O
Top	O
Company	O
Culture	O
List	O
2018	O
,	O
and	O
appeared	O
in	O
CNBC	O
's	O
2018	O
and	O
2019	O
"	O
Disruptor	O
50	O
"	O
lists	O
and	O
TIME	O
magazine	O
's	O
50	O
Genius	O
Companies	O
.	O
</s>
<s>
In	O
2019	O
,	O
Duolingo	B-Application
was	O
named	O
one	O
of	O
Forbes	O
's	O
"	O
Next	O
Billion-Dollar	O
Startups	O
2019	O
"	O
.	O
</s>
<s>
In	O
July	O
2020	O
,	O
Duolingo	B-Application
was	O
named	O
by	O
PCMag	O
as	O
"	O
The	O
Best	O
Free	O
Language	O
Learning	O
App	O
"	O
.	O
</s>
<s>
Due	O
to	O
the	O
app	O
's	O
sometimes	O
aggressive	O
sense	O
of	O
humor	O
and	O
attempts	O
to	O
ensure	O
learners	O
use	O
it	O
on	O
a	O
daily	O
basis	O
,	O
Duolingo	B-Application
's	O
mascot	O
,	O
a	O
green	O
cartoon	O
owl	B-Language
named	O
Duo	O
,	O
has	O
been	O
a	O
subject	O
of	O
an	O
Internet	O
meme	O
in	O
which	O
the	O
mascot	O
is	O
"	O
evil	O
"	O
and	O
will	O
stalk	O
and	O
threaten	O
users	O
if	O
they	O
do	O
not	O
keep	O
using	O
the	O
app	O
.	O
</s>
<s>
Acknowledging	O
the	O
meme	O
,	O
Duolingo	B-Application
released	O
a	O
video	O
on	O
April	O
Fool	O
's	O
Day	O
2019	O
;	O
the	O
video	O
depicts	O
a	O
new	O
feature	O
called	O
"	O
Duolingo	B-Application
Push	O
"	O
.	O
</s>
<s>
In	O
the	O
video	O
,	O
users	O
of	O
"	O
Duolingo	B-Application
Push	O
"	O
will	O
receive	O
reminders	O
to	O
use	O
the	O
app	O
in	O
person	O
by	O
Duo	O
himself	O
,	O
who	O
stares	O
at	O
users	O
and	O
follows	O
them	O
around	O
until	O
they	O
use	O
the	O
app	O
(	O
in	O
the	O
video	O
,	O
Duo	O
is	O
depicted	O
by	O
a	O
person	O
in	O
a	O
large	O
mascot	O
costume	O
)	O
.	O
</s>
<s>
On	O
April	O
1	O
,	O
2022	O
,	O
Duolingo	B-Application
released	O
another	O
video	O
in	O
the	O
form	O
of	O
a	O
spoof	O
legal	O
advertisement	O
where	O
the	O
lawyers	O
sue	O
the	O
company	O
for	O
damages	O
due	O
to	O
family	O
members	O
going	O
missing	O
,	O
once	O
again	O
alluding	O
to	O
the	O
meme	O
.	O
</s>
<s>
In	O
November	O
2019	O
,	O
Saturday	O
Night	O
Live	O
parodied	O
Duolingo	B-Application
in	O
a	O
sketch	O
in	O
which	O
adults	O
learn	O
to	O
communicate	O
with	O
children	O
using	O
a	O
fictitious	O
course	O
on	O
the	O
app	O
entitled	O
"	O
Duolingo	B-Application
for	O
Talking	O
to	O
Children	O
"	O
.	O
</s>
