<s>
GNUstep	B-Application
is	O
a	O
free	B-Application
software	I-Application
implementation	O
of	O
the	O
Cocoa	B-Operating_System
(	O
formerly	O
OpenStep	B-Operating_System
)	O
Objective-C	B-Language
frameworks	B-Architecture
,	O
widget	B-Library
toolkit	I-Library
,	O
and	O
application	O
development	O
tools	O
for	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
and	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
It	O
is	O
part	O
of	O
the	B-Application
GNU	I-Application
Project	I-Application
.	O
</s>
<s>
GNUstep	B-Application
features	O
a	O
cross-platform	B-Operating_System
,	O
object-oriented	B-Language
IDE	B-Application
.	O
</s>
<s>
Apart	O
from	O
the	O
default	O
Objective-C	B-Language
interface	O
,	O
GNUstep	B-Application
also	O
has	O
bindings	B-Application
for	O
Java	B-Language
,	O
Ruby	B-Language
,	O
GNU	B-Application
Guile	I-Application
and	O
Scheme	B-Language
.	O
</s>
<s>
The	O
GNUstep	B-Application
developers	O
track	O
some	O
additions	O
to	O
Apple	O
's	O
Cocoa	B-Operating_System
to	O
remain	O
compatible	O
.	O
</s>
<s>
The	O
roots	O
of	O
the	O
GNUstep	B-Application
application	O
interface	O
are	O
the	O
same	O
as	O
the	O
roots	O
of	O
Cocoa	B-Operating_System
:	O
NeXTSTEP	B-Application
and	O
OpenStep	B-Operating_System
.	O
</s>
<s>
GNUstep	B-Application
thus	O
predates	O
Cocoa	B-Operating_System
,	O
which	O
emerged	O
when	O
Apple	O
acquired	O
NeXT	O
's	O
technology	O
and	O
incorporated	O
it	O
into	O
the	O
development	O
of	O
the	O
original	O
Mac	B-Application
OS	I-Application
X	I-Application
,	O
while	O
GNUstep	B-Application
was	O
initially	O
an	O
effort	O
by	O
GNU	B-Application
developers	O
to	O
replicate	O
the	O
technically	O
ambitious	O
NeXTSTEP	B-Application
's	O
programmer-friendly	O
features	O
.	O
</s>
<s>
GNUstep	B-Application
began	O
when	O
Paul	O
Kunz	O
and	O
others	O
at	O
Stanford	O
Linear	O
Accelerator	O
Center	O
wanted	O
to	O
port	O
HippoDraw	B-Language
from	O
NeXTSTEP	B-Application
to	O
another	O
platform	O
.	O
</s>
<s>
Instead	O
of	O
rewriting	O
HippoDraw	B-Language
from	O
scratch	O
and	O
reusing	O
only	O
the	O
application	O
design	O
,	O
they	O
decided	O
to	O
rewrite	O
the	O
NeXTSTEP	B-Application
object	B-Language
layer	O
on	O
which	O
the	O
application	O
depended	O
.	O
</s>
<s>
It	O
enabled	O
them	O
to	O
port	O
HippoDraw	B-Language
to	O
Unix	O
systems	O
running	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
without	O
changing	O
a	O
single	O
line	O
of	O
their	O
application	O
source	O
.	O
</s>
<s>
After	O
the	O
OpenStep	B-Operating_System
specification	O
was	O
released	O
to	O
the	O
public	O
in	O
1994	O
,	O
they	O
decided	O
to	O
write	O
a	O
new	O
objcX	O
which	O
would	O
adhere	O
to	O
the	O
new	O
APIs	O
.	O
</s>
<s>
The	O
software	O
would	O
become	O
known	O
as	O
"	O
GNUstep	B-Application
"	O
.	O
</s>
<s>
GNUstep	B-Application
contains	O
a	O
set	O
of	O
graphical	O
control	O
elements	O
written	O
in	O
the	O
Objective-C	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
The	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
of	O
GNUMail	B-Language
is	O
composed	O
of	O
graphics	O
control	O
elements	O
.	O
</s>
<s>
GNUMail	B-Language
has	O
to	O
interact	O
with	O
the	O
windowing	B-Application
system	I-Application
,	O
e.g.	O
</s>
<s>
X11	B-Device
or	O
Wayland	B-Language
,	O
and	O
its	O
graphical	B-Application
user	I-Application
interface	I-Application
has	O
to	O
be	O
rendered	O
.	O
</s>
<s>
GNUstep	B-Application
's	O
backend	O
provides	O
a	O
small	O
set	O
of	O
functions	O
used	O
by	O
the	O
user	B-Application
interface	I-Application
library	O
to	O
interface	O
to	O
the	O
actual	O
windowing	B-Application
system	I-Application
.	O
</s>
<s>
It	O
also	O
has	O
a	O
rendering	O
engine	O
which	O
emulates	O
common	O
Postscript	B-Language
functions	O
.	O
</s>
<s>
The	O
package	O
gnustep-back	O
provides	O
the	O
following	O
backends	O
:	O
</s>
<s>
cairo	B-Language
–	O
default	O
backend	O
using	O
the	O
Cairo	B-Language
2D	O
graphics	O
library	O
.	O
</s>
<s>
winlib	O
–	O
default	O
backend	O
on	O
Microsoft	B-Application
Windows	I-Application
systems	O
.	O
</s>
<s>
Cairo	B-Language
and	O
Windows	B-Library
API	I-Library
variants	O
.	O
</s>
<s>
art	O
–	O
old	O
(	O
deprecated	O
)	O
backend	O
on	O
unix-like	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Uses	O
the	O
vector-based	O
PostScriptlike	O
2d	O
graphics	O
library	O
Libart	B-Language
.	O
</s>
<s>
xlib	B-Language
–	O
old	O
(	O
deprecated	O
)	O
X11	B-Device
backend	O
.	O
</s>
<s>
GNUstep	B-Application
inherits	O
some	O
design	O
principles	O
proposed	O
in	O
OPENSTEP	B-Operating_System
(	O
GNUstep	B-Application
predates	O
Cocoa	B-Operating_System
,	O
but	O
Cocoa	B-Operating_System
is	O
based	O
on	O
OPENSTEP	B-Operating_System
)	O
as	O
well	O
as	O
the	O
Objective-C	B-Language
language	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
Objective-C	B-Language
interface	O
,	O
some	O
small	O
projects	O
under	O
the	O
GNUstep	B-Application
umbrella	O
implement	O
other	O
APIs	O
from	O
Apple	O
:	O
</s>
<s>
The	O
Boron	O
library	O
aims	O
to	O
implement	O
the	O
Carbon	B-Operating_System
API	I-Operating_System
.	O
</s>
<s>
The	O
CoreBase	O
library	O
is	O
designed	O
to	O
be	O
compatible	O
with	O
Core	B-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
It	O
is	O
not	O
complete	O
enough	O
to	O
for	O
the	O
Base	O
(	O
Foundation	B-Operating_System
Kit	I-Operating_System
)	O
component	O
to	O
simply	O
be	O
a	O
wrapper	O
around	O
it	O
.	O
</s>
<s>
The	O
QuartzCore	O
library	O
implements	O
Core	B-Operating_System
Animation	I-Operating_System
APIs	O
.	O
</s>
<s>
The	O
Opal	O
library	O
implements	O
Quartz	B-Operating_System
2D	I-Operating_System
.	O
</s>
<s>
,	O
there	O
are	O
no	O
projects	O
that	O
build	O
the	O
Swift	B-Application
programming	I-Application
language	I-Application
against	O
the	O
GNUstep	B-Application
Objective-C	B-Language
environment	O
.	O
</s>
<s>
Here	O
are	O
some	O
examples	O
of	O
applications	O
written	O
for	O
or	O
ported	O
to	O
GNUstep	B-Application
.	O
</s>
<s>
ProjectCenter	O
,	O
the	O
Project	B-Operating_System
Builder	I-Operating_System
or	O
Xcode	B-Operating_System
equivalent	O
.	O
</s>
<s>
Universal	B-Device
Windows	I-Device
Platform	I-Device
,	O
which	O
includes	O
a	O
WinObjC	O
suite	O
consisting	O
of	O
various	O
parts	O
of	O
GNUstep	B-Application
and	O
Microsoft	O
's	O
own	O
implementations	O
of	O
things	O
like	O
the	O
Cocoa	B-Operating_System
Touch	I-Operating_System
API	O
.	O
</s>
<s>
The	O
Foundation	B-Operating_System
Kit	I-Operating_System
provides	O
basic	O
classes	O
such	O
as	O
wrapper	O
classes	O
and	O
data	O
structure	O
classes	O
.	O
</s>
<s>
The	O
Application	B-Operating_System
Kit	I-Operating_System
provides	O
classes	O
oriented	O
around	O
graphical	B-Application
user	I-Application
interface	I-Application
capabilities	O
.	O
</s>
