<s>
Public-domain	B-Application
software	I-Application
is	O
software	O
that	O
has	O
been	O
placed	O
in	O
the	O
public	O
domain	O
,	O
in	O
other	O
words	O
,	O
software	O
for	O
which	O
there	O
is	O
absolutely	O
no	O
ownership	O
such	O
as	O
copyright	O
,	O
trademark	O
,	O
or	O
patent	O
.	O
</s>
<s>
This	O
kind	O
of	O
freely	O
distributed	O
and	O
shared	O
"	O
free	O
software	O
"	O
combined	O
the	O
present-day	O
classes	O
of	O
freeware	B-License
,	O
shareware	B-License
,	O
and	O
free	B-License
and	I-License
open-source	I-License
software	I-License
,	O
and	O
was	O
created	O
in	O
academia	O
,	O
by	O
hobbyists	O
,	O
and	O
hackers	O
.	O
</s>
<s>
PD	B-Application
software	I-Application
was	O
also	O
shared	O
and	O
distributed	O
as	O
printed	O
source	O
code	O
(	O
type-in	O
programs	O
)	O
in	O
computer	O
magazines	O
(	O
like	O
Creative	O
Computing	O
,	O
SoftSide	O
,	O
Compute	O
!,	O
Byte	O
,	O
etc	O
.	O
)	O
</s>
<s>
and	O
books	O
,	O
like	O
the	O
bestseller	O
BASIC	B-Application
Computer	I-Application
Games	I-Application
.	O
</s>
<s>
Earlier	O
on	O
,	O
closed-source	B-Application
software	I-Application
was	O
uncommon	O
until	O
the	O
mid-1970s	O
to	O
1980s	O
.	O
</s>
<s>
This	O
legislation	O
,	O
plus	O
court	O
decisions	O
such	O
as	O
Apple	B-Device
v	I-Device
.	I-Device
Franklin	I-Device
in	O
1983	O
for	O
object	B-Language
code	I-Language
,	O
clarified	O
that	O
the	O
Copyright	O
Act	O
gave	O
computer	O
programs	O
the	O
copyright	O
status	O
of	O
literary	O
works	O
.	O
</s>
<s>
In	O
the	O
1980s	O
,	O
a	O
common	O
way	O
to	O
share	O
public-domain	B-Application
software	I-Application
was	O
by	O
receiving	O
them	O
through	O
a	O
local	O
user	O
group	O
or	O
a	O
company	O
like	O
PC-SIG	O
of	O
Sunnyvale	O
,	O
California	O
,	O
which	O
maintained	O
a	O
mail-order	O
catalog	O
of	O
more	O
than	O
300	O
disks	O
with	O
an	O
average	O
price	O
of	O
US$6	O
.	O
</s>
<s>
Public-domain	B-Application
software	I-Application
with	O
source	O
code	O
was	O
also	O
shared	O
on	O
BBS	B-Application
networks	O
.	O
</s>
<s>
Public-domain	B-Application
software	I-Application
was	O
commercialized	O
sometimes	O
by	O
a	O
donationware	B-License
model	O
,	O
asking	O
the	O
users	O
for	O
a	O
financial	O
donation	O
to	O
be	O
sent	O
by	O
mail	O
.	O
</s>
<s>
The	O
public-domain	O
"	O
free	O
sharing	O
"	O
and	O
donationware	B-License
commercialization	O
models	O
evolved	O
in	O
the	O
following	O
years	O
to	O
the	O
(	O
non-voluntary	O
)	O
shareware	B-License
model	O
,	O
and	O
software	O
free	O
of	O
charge	O
,	O
called	O
freeware	B-License
.	O
</s>
<s>
With	O
the	O
Berne	O
Convention	O
Implementation	O
Act	O
of	O
1988	O
(	O
and	O
the	O
earlier	O
Copyright	O
Act	O
of	O
1976	O
)	O
,	O
the	O
legal	O
basis	O
for	O
public-domain	B-Application
software	I-Application
changed	O
drastically	O
.	O
</s>
<s>
With	O
the	O
new	O
act	O
,	O
software	O
was	O
by	O
default	O
copyright-protected	O
and	O
needed	O
an	O
explicit	O
waiver	O
statement	O
or	O
license	B-License
from	O
the	O
author	O
.	O
</s>
<s>
Reference	O
implementations	O
of	O
algorithms	O
,	O
often	O
cryptographic	O
meant	O
or	O
applied	O
for	O
standardization	O
are	O
still	O
often	O
released	O
into	O
the	O
public	O
domain	O
;	O
examples	O
include	O
CERN	B-Application
httpd	I-Application
in	O
1993	O
and	O
Serpent	B-Algorithm
cipher	O
in	O
1999	O
.	O
</s>
<s>
The	O
Openwall	B-Application
Project	I-Application
maintains	O
a	O
list	O
of	O
several	O
algorithms	O
and	O
their	O
source	O
code	O
in	O
the	O
public	O
domain	O
.	O
</s>
<s>
As	O
a	O
response	O
of	O
the	O
academic	O
software	O
ecosystem	O
to	O
the	O
change	O
in	O
the	O
copyright	O
system	O
in	O
the	O
late	O
1980s	O
,	O
permissive	B-License
license	I-License
texts	O
were	O
developed	O
,	O
like	O
the	O
BSD	B-Operating_System
license	I-Operating_System
and	O
its	O
derivatives	O
.	O
</s>
<s>
Permissive-licensed	O
software	O
,	O
which	O
is	O
a	O
kind	O
of	O
free	B-License
and	I-License
open-source	I-License
software	I-License
,	O
shares	O
most	O
characteristics	O
of	O
earlier	O
public-domain	B-Application
software	I-Application
but	O
stands	O
on	O
the	O
legal	O
basis	O
of	O
copyright	O
law	O
.	O
</s>
<s>
In	O
the	O
1980s	O
Richard	O
Stallman	O
,	O
who	O
for	O
long	O
worked	O
in	O
an	O
academic	O
environment	O
of	O
"	O
public-domain	O
"	O
-like	O
software	O
sharing	O
,	O
noticed	O
the	O
emergence	O
of	O
proprietary	B-Application
software	I-Application
and	O
the	O
decline	O
of	O
the	O
public-domain	B-Application
software	I-Application
ecosystem	O
.	O
</s>
<s>
In	O
an	O
effort	O
to	O
preserve	O
this	O
ecosystem	O
he	O
created	O
a	O
software	B-License
license	I-License
,	O
the	O
GPL	B-License
,	O
which	O
encodes	O
the	O
public-domain	O
rights	O
and	O
enforces	O
them	O
irrevocably	O
on	O
software	O
.	O
</s>
<s>
Paradoxically	O
,	O
his	O
copyleft	B-License
approach	O
relies	O
on	O
the	O
enforceability	O
of	O
the	O
copyright	O
to	O
be	O
effective	O
.	O
</s>
<s>
Copyleft	B-License
free	O
software	O
,	O
therefore	O
,	O
shares	O
many	O
properties	O
with	O
public-domain	B-Application
software	I-Application
,	O
but	O
does	O
not	O
allow	O
relicensing	O
or	O
sublicensing	O
.	O
</s>
<s>
Unlike	O
real	O
public-domain	B-Application
software	I-Application
or	O
permissive-licensed	O
software	O
,	O
Stallman	O
's	O
copyleft	B-License
license	I-License
tries	O
to	O
enforce	O
the	O
free	O
shareability	O
of	O
software	O
also	O
for	O
the	O
future	O
by	O
not	O
allowing	O
license	B-License
changes	O
.	O
</s>
<s>
To	O
refer	O
to	O
free	O
software	O
(	O
which	O
is	O
under	O
a	O
free	B-License
software	I-License
license	I-License
)	O
or	O
to	O
software	O
distributed	O
and	O
usable	O
free	O
of	O
charge	O
(	O
freeware	B-License
)	O
as	O
"	O
public-domain	O
"	O
is	O
therefore	O
incorrect	O
.	O
</s>
<s>
copyright	O
)	O
,	O
in	O
free	O
software	O
the	O
author	O
's	O
copyright	O
is	O
still	O
retained	O
and	O
used	O
,	O
for	O
instance	O
,	O
to	O
enforce	O
copyleft	B-License
or	O
to	O
hand	O
out	O
permissive-licensed	O
software	O
.	O
</s>
<s>
Another	O
distinct	O
difference	O
is	O
that	O
an	O
executable	B-Application
program	I-Application
may	O
be	O
in	O
the	O
public	O
domain	O
even	O
if	O
its	O
source	O
code	O
is	O
not	O
made	O
available	O
(	O
making	O
the	O
program	O
not	O
feasibly	O
modifiable	O
)	O
,	O
while	O
free	O
software	O
always	O
has	O
the	O
source	O
code	O
available	O
.	O
</s>
<s>
With	O
the	O
2000s	O
and	O
the	O
emergence	O
of	O
peer-to-peer	O
sharing	O
networks	O
and	O
sharing	O
in	O
web	O
development	O
,	O
a	O
new	O
copyright-critical	O
generation	O
of	O
developers	O
made	O
the	O
"	O
license-free	B-License
"	O
public-domain	B-Application
software	I-Application
model	O
visible	O
again	O
,	O
also	O
criticizing	O
the	O
FOSS	B-License
license	B-License
ecosystem	O
(	O
"	O
Post	B-Application
Open	I-Application
Source	I-Application
"	O
)	O
as	O
stabilizing	O
part	O
of	O
the	O
copyright	O
system	O
.	O
</s>
<s>
New	O
non-FOSS	O
licenses	O
and	O
waiver	O
texts	O
were	O
developed	O
,	O
notably	O
the	O
Creative	O
Commons	O
"	O
CC0	O
"	O
(	O
2009	O
)	O
and	O
the	O
"	O
Unlicense	B-License
"	O
(	O
2010	O
)	O
,	O
and	O
there	O
was	O
a	O
noticeable	O
rise	O
in	O
the	O
popularity	O
of	O
permissive	B-License
software	I-License
licenses	I-License
.	O
</s>
<s>
Around	O
2004	O
,	O
there	O
was	O
debate	O
on	O
whether	O
public-domain	B-Application
software	I-Application
could	O
be	O
considered	O
part	O
of	O
the	O
FOSS	B-License
ecosystem	O
,	O
as	O
argued	O
by	O
lawyer	O
Lawrence	O
Rosen	O
in	O
the	O
essay	O
"	O
Why	O
the	O
public	O
domain	O
is	O
n't	O
a	O
license	B-License
"	O
,	O
a	O
position	O
that	O
faced	O
opposition	O
by	O
Daniel	O
J	O
.	O
Bernstein	O
and	O
others	O
.	O
</s>
<s>
In	O
2012	O
,	O
the	O
status	O
was	O
finally	O
resolved	O
when	O
Rosen	O
changed	O
his	O
mind	O
and	O
accepted	O
the	O
CC0	O
as	O
an	O
open-source	O
license	B-License
,	O
while	O
admitting	O
that	O
,	O
contrary	O
to	O
previous	O
claims	O
,	O
copyright	O
could	O
be	O
waived	O
,	O
as	O
backed	O
by	O
a	O
Ninth	O
Circuit	O
decision	O
.	O
</s>
<s>
While	O
real	O
public	O
domain	O
makes	O
software	B-License
licenses	I-License
unnecessary	O
,	O
as	O
no	O
owner/author	O
is	O
required	O
to	O
grant	O
permission	O
(	O
"	O
Permission	O
culture	O
"	O
)	O
,	O
there	O
are	O
licenses	O
that	O
grant	O
public-domain-like	O
rights	O
.	O
</s>
<s>
There	O
is	O
no	O
universally	O
agreed-upon	O
license	B-License
,	O
but	O
there	O
are	O
multiple	O
licenses	O
that	O
aim	O
to	O
release	O
source	O
code	O
into	O
the	O
public	O
domain	O
.	O
</s>
<s>
In	O
2000	O
the	O
WTFPL	B-License
was	O
released	O
as	O
a	O
public-domain-like	O
license/waiver/anti	O
-copyright	O
notice	O
.	O
</s>
<s>
This	O
is	O
achieved	O
by	O
a	O
public	O
domain	O
waiver	O
statement	O
and	O
a	O
fallback	O
all-permissive	B-License
license	I-License
,	O
in	O
case	O
the	O
waiver	O
is	O
not	O
possible	O
.	O
</s>
<s>
The	B-License
Unlicense	I-License
,	O
published	O
around	O
2010	O
,	O
has	O
a	O
focus	O
on	O
an	O
anti-copyright	O
message	O
.	O
</s>
<s>
The	B-License
Unlicense	I-License
offers	O
a	O
public	O
domain	O
waiver	O
text	O
with	O
a	O
fallback	O
public-domain-like	O
license	B-License
inspired	O
by	O
permissive	B-License
licenses	I-License
but	O
without	O
attribution	O
clause	O
.	O
</s>
<s>
In	O
2015	O
,	O
GitHub	B-Application
reported	O
that	O
of	O
the	O
approximately	O
5.1	O
million	O
licensed	O
projects	O
it	O
hosted	O
,	O
almost	O
2%	O
used	O
the	B-License
Unlicense	I-License
.	O
</s>
<s>
Another	O
popular	O
option	O
is	O
the	O
Zero	O
Clause	O
BSD	B-Operating_System
license	I-Operating_System
,	O
released	O
in	O
2006	O
and	O
aimed	O
at	O
software	O
.	O
</s>
<s>
As	O
result	O
,	O
such	O
licensed	O
public-domain	B-Application
software	I-Application
has	O
all	O
the	O
four	O
freedoms	O
but	O
is	O
not	O
hampered	O
by	O
the	O
complexities	O
of	O
attribution	O
(	O
restriction	O
of	O
permissive	O
licensed	O
software	O
)	O
or	O
license	B-License
compatibility	O
(	O
issue	O
with	O
copyleft	B-License
licensed	O
software	O
)	O
.	O
</s>
<s>
Public	B-Application
domain	I-Application
software	I-Application
in	O
the	O
early	O
computer	O
age	O
was	O
,	O
for	O
instance	O
,	O
shared	O
as	O
type-in	O
programs	O
in	O
computer	O
magazines	O
and	O
books	O
like	O
BASIC	B-Application
Computer	I-Application
Games	I-Application
.	O
</s>
<s>
Explicit	O
PD	O
waiver	O
statements	O
or	O
license	B-License
files	O
were	O
at	O
that	O
time	O
unusual	O
.	O
</s>
<s>
Publicly	O
available	O
software	O
without	O
a	O
copyright	O
notice	O
was	O
assumed	O
to	O
be	O
,	O
and	O
shared	O
as	O
,	O
public-domain	B-Application
software	I-Application
.	O
</s>
<s>
Notable	O
general	O
PD	B-Application
software	I-Application
from	O
that	O
time	O
include	O
:	O
</s>
<s>
Video	O
games	O
are	O
among	O
the	O
earliest	O
examples	O
of	O
shared	O
PD	B-Application
software	I-Application
,	O
which	O
are	O
still	O
notable	O
today	O
:	O
</s>
<s>
Spacewar	B-Application
!	I-Application
</s>
<s>
Many	O
PD	B-Application
software	I-Application
authors	O
kept	O
the	O
practices	O
of	O
public-domain	O
release	O
without	O
having	O
a	O
waiver	O
text	O
,	O
not	O
knowing	O
or	O
caring	O
for	O
the	O
changed	O
copyright	O
law	O
,	O
thus	O
creating	O
a	O
legal	O
problem	O
.	O
</s>
<s>
Only	O
slowly	O
did	O
PD	B-Application
software	I-Application
authors	O
start	O
to	O
include	O
explicit	O
relinquishment	O
or	O
license	B-License
statement	O
texts	O
.	O
</s>
<s>
These	O
examples	O
of	O
modern	O
PD	B-Application
software	I-Application
(	O
after	O
the	O
Berne	O
Convention	O
Implementation	O
Act	O
of	O
1988	O
)	O
are	O
either	O
under	O
proper	O
public	O
domain	O
(	O
e.g.	O
</s>
<s>
created	O
by	O
a	O
US	O
governmental	O
organization	O
)	O
,	O
under	O
a	O
proper	O
public	O
domain	O
like	O
license	B-License
(	O
for	O
instance	O
CC0	O
)	O
,	O
or	O
accompanied	O
by	O
a	O
clear	O
waiver	O
statement	O
from	O
the	O
author	O
.	O
</s>
<s>
Whilst	O
not	O
as	O
widespread	O
as	O
in	O
the	O
pre-2000s	O
,	O
PD	B-Application
software	I-Application
still	O
exists	O
nowadays	O
.	O
</s>
<s>
For	O
example	O
,	O
SourceForge	B-Application
listed	O
334	O
hosted	O
PD	O
projects	O
in	O
2016	O
,	O
and	O
GitHub	B-Application
102,000	O
under	O
the	B-License
Unlicense	I-License
alone	O
in	O
2015	O
.	O
</s>
<s>
In	O
2016	O
,	O
an	O
analysis	O
of	O
the	O
Fedora	O
Project	O
's	O
packages	O
revealed	O
PD	O
was	O
the	O
seventh	O
most	O
popular	O
"	O
license	B-License
"	O
.	O
</s>
