<s>
Squeak	B-Operating_System
is	O
an	O
object-oriented	B-Language
,	O
class-based	O
,	O
and	O
reflective	B-Language
programming	I-Language
language	O
.	O
</s>
<s>
It	O
was	O
derived	O
from	O
Smalltalk-80	B-Application
by	O
a	O
group	O
that	O
included	O
some	O
of	O
Smalltalk-80	B-Application
'	O
s	O
original	O
developers	O
,	O
initially	O
at	O
Apple	O
Computer	O
,	O
then	O
at	O
Walt	O
Disney	O
Imagineering	O
,	O
where	O
it	O
was	O
intended	O
for	O
use	O
in	O
internal	O
Disney	O
projects	O
.	O
</s>
<s>
The	O
group	O
would	O
later	O
go	O
on	O
to	O
be	O
supported	O
by	O
HP	O
labs	O
,	O
SAP	B-Application
,	O
and	O
most	O
recently	O
,	O
Y	O
Combinator	O
.	O
</s>
<s>
Squeak	B-Operating_System
runs	O
on	O
a	O
virtual	B-Architecture
machine	I-Architecture
(	O
VM	O
)	O
,	O
allowing	O
for	O
a	O
high	O
degree	O
of	O
portability	O
.	O
</s>
<s>
The	O
Squeak	B-Operating_System
system	O
includes	O
code	O
for	O
generating	O
a	O
new	O
version	O
of	O
the	O
VM	O
on	O
which	O
it	O
runs	O
,	O
along	O
with	O
a	O
VM	O
simulator	O
written	O
in	O
Squeak	B-Operating_System
.	O
</s>
<s>
Dan	O
Ingalls	O
,	O
an	O
important	O
contributor	O
to	O
the	O
Squeak	B-Operating_System
project	O
,	O
wrote	O
the	O
paper	O
upon	O
which	O
Squeak	B-Operating_System
is	O
built	O
,	O
and	O
constructed	O
the	O
architecture	O
for	O
five	O
generations	O
of	O
the	O
Smalltalk	B-Application
language	O
.	O
</s>
<s>
Alan	O
Kay	O
is	O
an	O
important	O
contributor	O
to	O
the	O
Squeak	B-Operating_System
project	O
,	O
and	O
Squeak	B-Operating_System
incorporates	O
many	O
elements	O
of	O
his	O
proposed	O
Dynabook	B-General_Concept
concept	O
.	O
</s>
<s>
Squeak	B-Operating_System
includes	O
four	O
user	B-Application
interface	I-Application
frameworks	O
:	O
</s>
<s>
An	O
implementation	O
of	O
Morphic	O
,	O
Self	B-Operating_System
's	I-Operating_System
graphical	O
direct	O
manipulation	O
interface	O
framework	O
.	O
</s>
<s>
This	O
is	O
Squeak	B-Operating_System
's	O
main	O
interface	O
.	O
</s>
<s>
Tile-based	O
,	O
limited	O
visual	B-Language
programming	I-Language
scripting	O
in	O
Etoys	B-Application
,	O
based	O
on	O
Morphic	O
.	O
</s>
<s>
A	O
novel	O
,	O
experimental	O
interface	O
called	O
Tweak	B-Application
.	O
</s>
<s>
In	O
2001	O
it	O
became	O
clear	O
that	O
the	O
Etoy	O
architecture	O
in	O
Squeak	B-Operating_System
had	O
reached	O
its	O
limits	O
in	O
what	O
the	O
Morphic	O
interface	O
infrastructure	O
could	O
do	O
.	O
</s>
<s>
Hewlett-Packard	O
researcher	O
Andreas	B-Operating_System
Raab	I-Operating_System
proposed	O
defining	O
a	O
"	O
script	O
process	O
"	O
and	O
providing	O
a	O
default	O
scheduling-mechanism	O
that	O
avoids	O
several	O
more	O
general	O
problems	O
.	O
</s>
<s>
This	O
resulted	O
in	O
a	O
new	O
user	B-Application
interface	I-Application
,	O
proposed	O
to	O
replace	O
the	O
Squeak	B-Operating_System
Morphic	O
user	B-Application
interface	I-Application
in	O
the	O
future	O
.	O
</s>
<s>
Tweak	B-Application
added	O
mechanisms	O
of	O
islands	O
,	O
asynchronous	O
messaging	O
,	O
players	O
and	O
costumes	O
,	O
language	O
extensions	O
,	O
projects	O
,	O
and	O
tile	O
scripting	O
.	O
</s>
<s>
Its	O
underlying	O
object	B-Language
system	I-Language
is	O
class-based	O
,	O
but	O
to	O
users	O
,	O
during	O
programming	O
(	O
scripting	O
)	O
,	O
it	O
acts	O
like	O
it	O
is	O
prototype-based	B-Application
.	O
</s>
<s>
Tweak	B-Application
objects	O
are	O
created	O
and	O
run	O
in	O
Tweak	B-Application
project	O
windows	B-Application
.	O
</s>
<s>
A	O
model	O
–	O
view	O
–	O
controller	O
(	O
MVC	O
)	O
interface	O
was	O
the	O
primary	O
UI	O
in	O
Squeak	B-Operating_System
versions	O
3.8	O
and	O
earlier	O
.	O
</s>
<s>
It	O
derived	O
from	O
the	O
original	O
Smalltalk-80	B-Application
user	B-Application
interface	I-Application
framework	O
which	O
first	O
introduced	O
and	O
popularized	O
the	O
MVC	O
architectural	O
pattern	O
.	O
</s>
<s>
Thus	O
,	O
the	O
term	O
"	O
MVC	O
"	O
in	O
the	O
context	O
of	O
Squeak	B-Operating_System
refers	O
to	O
both	O
one	O
of	O
the	O
available	O
user	B-Application
interface	I-Application
frameworks	O
and	O
the	O
pattern	O
the	O
framework	O
follows	O
.	O
</s>
<s>
Many	O
Squeak	B-Operating_System
contributors	O
collaborate	O
on	O
Open	B-Protocol
Cobalt	I-Protocol
,	O
a	O
free	B-License
and	I-License
open	I-License
source	I-License
virtual	B-Application
world	I-Application
browser	O
and	O
construction	O
toolkit	O
built	O
on	O
Squeak	B-Operating_System
.	O
</s>
<s>
was	O
implemented	O
in	O
Squeak	B-Operating_System
.	O
</s>
<s>
OpenQwaq	B-Application
,	O
a	O
virtual	O
conferencing	O
and	O
collaboration	O
system	O
,	O
is	O
based	O
on	O
Squeak	B-Operating_System
.	O
</s>
<s>
Squeak	B-Operating_System
4.0	O
and	O
later	O
may	O
be	O
downloaded	O
at	O
no	O
cost	O
,	O
including	O
source	O
code	O
,	O
as	O
a	O
prebuilt	O
virtual	B-Architecture
machine	I-Architecture
image	O
licensed	O
under	O
the	B-License
MIT	I-License
License	I-License
,	O
with	O
the	O
exception	O
of	O
some	O
of	O
the	O
original	O
Apple	O
code	O
,	O
which	O
is	O
governed	O
by	O
the	O
Apache	B-Application
License	I-Application
.	O
</s>
<s>
Squeak	B-Operating_System
was	O
originally	O
released	O
by	O
Apple	O
under	O
its	O
own	O
Squeak	B-Operating_System
License	O
.	O
</s>
<s>
While	O
source	O
code	O
was	O
available	O
and	O
modification	O
permitted	O
,	O
the	O
Squeak	B-Operating_System
License	O
contained	O
an	O
indemnity	O
clause	O
that	O
prevented	O
it	O
from	O
qualifying	O
as	O
true	O
free	B-License
and	I-License
open-source	I-License
software	I-License
.	O
</s>
<s>
In	O
2006	O
,	O
Apple	O
relicensed	O
Squeak	B-Operating_System
twice	O
.	O
</s>
<s>
First	O
,	O
in	O
May	O
,	O
Apple	O
used	O
its	O
own	O
Apple	B-License
Public	I-License
Source	I-License
License	I-License
,	O
which	O
satisfies	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
's	O
concept	O
of	O
a	O
Free	B-Application
Software	I-Application
License	O
and	O
has	O
attained	O
official	O
approval	O
from	O
the	O
Open	B-Application
Source	I-Application
Initiative	O
as	O
an	O
Open	B-Application
Source	I-Application
License	O
.	O
</s>
<s>
However	O
,	O
The	O
Apple	B-License
Public	I-License
Source	I-License
License	I-License
fails	O
to	O
conform	O
to	O
the	O
Debian	B-License
Free	I-License
Software	I-License
Guidelines	I-License
.	O
</s>
<s>
To	O
enable	O
inclusion	O
of	O
Etoys	B-Application
in	O
the	O
One	O
Laptop	O
Per	O
Child	O
project	O
,	O
a	O
second	O
relicensing	O
was	O
undertaken	O
using	O
the	O
Apache	B-Application
License	I-Application
.	O
</s>
<s>
At	O
this	O
point	O
,	O
an	O
effort	O
was	O
also	O
made	O
to	O
address	O
the	O
issue	O
of	O
code	O
contributed	O
by	O
members	O
of	O
the	O
Squeak	B-Operating_System
community	O
,	O
which	O
it	O
was	O
not	O
in	O
Apple	O
's	O
power	O
to	O
unilaterally	O
relicense	O
.	O
</s>
<s>
For	O
each	O
contribution	O
made	O
under	O
the	O
Squeak	B-Operating_System
License	O
since	O
1996	O
,	O
a	O
relicensing	O
statement	O
was	O
obtained	O
authorizing	O
distribution	O
under	O
the	B-License
MIT	I-License
license	I-License
,	O
and	O
finally	O
in	O
March	O
2010	O
,	O
the	O
end	O
result	O
was	O
released	O
as	O
Squeak	B-Operating_System
4.0	O
,	O
now	O
under	O
combined	O
MIT	B-License
and	O
Apache	B-Application
licenses	I-Application
.	O
</s>
<s>
The	O
Squeak	B-Operating_System
virtual	B-Architecture
machine	I-Architecture
is	O
a	O
family	O
of	O
virtual	B-Architecture
machines	I-Architecture
(	O
VMs	O
)	O
used	O
in	O
Smalltalk	B-Application
programming	I-Application
language	I-Application
implementations	O
.	O
</s>
<s>
They	O
are	O
an	O
essential	O
part	O
of	O
any	O
Smalltalk	B-Application
implementation	O
.	O
</s>
<s>
All	O
are	O
open-source	B-Application
software	I-Application
.	O
</s>
