<s>
Alien	B-Application
Arena	I-Application
(	O
initially	O
CodeRED	B-Application
:	I-Application
Alien	I-Application
Arena	I-Application
)	O
is	O
a	O
free	B-License
,	O
stand-alone	O
first-person	O
shooter	O
computer	O
game	O
.	O
</s>
<s>
Begun	O
by	O
COR	B-Application
Entertainment	I-Application
in	O
2004	O
,	O
the	O
game	O
combines	O
a	O
1950s-era	O
sci-fi	O
atmosphere	O
with	O
gameplay	O
similar	O
to	O
the	O
Quake	B-Application
,	O
Doom	B-Application
,	O
and	O
Unreal	B-Operating_System
Tournament	I-Operating_System
series	O
.	O
</s>
<s>
Alien	B-Application
Arena	I-Application
focuses	O
mainly	O
on	O
online	B-Application
multiplayer	O
action	O
,	O
although	O
it	O
does	O
contain	O
single-player	O
matches	O
against	O
bots	O
.	O
</s>
<s>
Alien	B-Application
Arena	I-Application
has	O
been	O
released	O
for	O
Microsoft	B-Application
Windows	I-Application
,	O
OS	B-Operating_System
X	I-Operating_System
,	O
Linux	B-Application
,	O
and	O
FreeBSD	B-Operating_System
.	O
</s>
<s>
While	O
the	O
game	O
's	O
content	O
is	O
proprietary	B-License
freeware	I-License
,	O
prohibiting	O
commercial	O
re-sale	O
,	O
the	O
CRX	O
engine	O
is	O
open	B-Application
source	I-Application
.	O
</s>
<s>
In	O
2013	O
the	O
assets	O
license	B-License
was	O
loosened	O
somewhat	O
,	O
which	O
allowed	O
the	O
game	O
package	O
to	O
be	O
included	O
in	O
certain	O
Linux	B-Application
distributions	I-Application
,	O
such	O
as	O
Fedora	O
,	O
Debian	O
and	O
Ubuntu	B-Operating_System
.	O
</s>
<s>
The	O
game	O
features	O
an	O
internal	O
server	O
browser	O
for	O
finding	O
other	O
players	O
online	B-Application
,	O
and	O
the	O
external	O
Galaxy	O
program	O
performs	O
the	O
same	O
function	O
without	O
having	O
to	O
launch	O
the	O
game	O
,	O
akin	O
to	O
The	B-Application
All-Seeing	I-Application
Eye	I-Application
.	O
</s>
<s>
It	O
also	O
serves	O
as	O
an	O
IRC	B-Protocol
client	B-Protocol
for	O
chat	O
between	O
players	O
.	O
</s>
<s>
The	O
game	O
uses	O
modified	O
Quake	B-Application
II	O
physics	O
.	O
</s>
<s>
Most	O
Quake	B-Application
II	O
trickjumps	O
,	O
such	O
as	O
strafejumping	O
,	O
will	O
work	O
in	O
Alien	B-Application
Arena	I-Application
.	O
</s>
<s>
However	O
,	O
dodging	O
,	O
which	O
is	O
n't	O
found	O
in	O
Quake	B-Application
II	O
,	O
has	O
also	O
been	O
added	O
to	O
the	O
game	O
.	O
</s>
<s>
Although	O
it	O
had	O
been	O
in	O
development	O
since	O
2003	O
,	O
Alien	B-Application
Arena	I-Application
was	O
first	O
released	O
as	O
a	O
beta	O
in	O
August	O
2004	O
,	O
with	O
the	O
title	O
CodeRED	B-Application
:	I-Application
Alien	I-Application
Arena	I-Application
.	O
</s>
<s>
Following	O
these	O
games	O
,	O
Alien	B-Application
Arena	I-Application
received	O
greater	O
development	O
focus	O
.	O
</s>
<s>
The	O
"	O
CodeRED	O
"	O
title	O
continued	O
to	O
be	O
used	O
until	O
Alien	B-Application
Arena	I-Application
2006	O
was	O
released	O
in	O
November	O
2005	O
,	O
promoted	O
as	O
a	O
"	O
sequel	O
"	O
to	O
the	O
old	O
CodeRED	O
version	O
.	O
</s>
<s>
In	O
September	O
2012	O
,	O
Alien	B-Application
Arena	I-Application
was	O
also	O
made	O
available	O
as	O
an	O
online	B-Application
version	O
through	O
Roozz	O
.	O
</s>
<s>
By	O
installing	O
a	O
small	O
plugin	O
,	O
players	O
can	O
play	O
the	O
game	O
in	O
any	O
browser	O
on	O
the	O
Windows	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
The	O
game	O
is	O
powered	O
by	O
the	O
id	O
Tech	O
2-based	O
CRX	O
game	O
engine	O
,	O
which	O
has	O
been	O
rewritten	O
to	O
include	O
support	O
for	O
such	O
features	O
as	O
32-bit	O
high-resolution	B-Algorithm
textures	O
,	O
3D	O
models	O
used	O
as	O
architecture	O
in	O
maps	O
,	O
GLSL	B-Language
per-pixel	O
lighting	O
effects	O
,	O
parallax	O
mapping	O
,	O
normal	B-Application
mapping	I-Application
,	O
ragdoll	O
physics	O
using	O
the	O
Open	B-Application
Dynamics	I-Application
Engine	I-Application
,	O
server-side	O
antilag	B-Application
code	O
,	O
shaders	O
(	O
GLSL	B-Language
and	O
rscript	O
)	O
,	O
textured	O
particles	O
,	O
semi-true	O
reflective	O
water	O
with	O
per-pixel	O
distortion	O
shaders	O
,	O
reflective	O
surfaces	O
on	O
entities	O
,	O
light	O
bloom	O
,	O
real-time	O
shadows	O
,	O
overbright	O
bits	O
,	O
real-time	O
vertex	B-Algorithm
lighting	I-Algorithm
,	O
and	O
other	O
graphical	O
effects	O
,	O
all	O
of	O
which	O
can	O
be	O
turned	O
on	O
or	O
off	O
in	O
the	O
menu	O
.	O
</s>
<s>
As	O
of	O
CRX	O
version	O
7.30	O
,	O
OpenAL	B-Application
is	O
used	O
for	O
sound	O
on	O
all	O
platforms	O
.	O
</s>
<s>
Physics	O
support	O
was	O
added	O
in	O
version	O
7.50	O
using	O
the	O
Open	B-Application
Dynamics	I-Application
Engine	I-Application
.	O
</s>
<s>
Alien	B-Application
Arena	I-Application
has	O
been	O
compared	O
to	O
Quake	B-Application
III	I-Application
and	O
Unreal	B-Operating_System
Tournament	I-Operating_System
,	O
and	O
is	O
considered	O
one	O
of	O
the	O
best	O
free	B-Application
first-person	I-Application
shooters	I-Application
.	O
</s>
<s>
In	O
2008	O
APCMag.com	O
named	O
Alien	B-Application
Arena	I-Application
among	O
the	O
Top	O
5	O
best	O
(	O
free	B-License
)	O
open	B-Application
source	I-Application
games	O
.	O
</s>
<s>
In	O
a	O
2009	O
review	O
of	O
Linux	B-Application
Format	O
Alien	B-Application
Arena	I-Application
was	O
rated	O
8/10	O
.	O
</s>
<s>
Alien	B-Application
Arena	I-Application
was	O
selected	O
in	O
February	O
2014	O
as	O
"	O
HotPick	O
"	O
by	O
Linux	B-Application
Format	O
.	O
</s>
<s>
On	O
November	O
3	O
,	O
2017	O
COR	B-Application
Entertainment	I-Application
released	O
Alien	B-Application
Arena	I-Application
:	O
Warriors	O
of	O
Mars	O
on	O
Steam	O
for	O
Windows	O
and	O
Linux	B-Application
platforms	O
.	O
</s>
