<s>
Zombie	B-Application
Panic	I-Application
!	I-Application
</s>
<s>
Source	O
is	O
a	O
cooperative	O
survival-horror	O
Half-Life	B-Application
2	I-Application
first-person	O
shooter	O
modification	O
.	O
</s>
<s>
It	O
is	O
the	O
sequel	O
to	O
the	O
Half-Life	B-Application
mod	O
Zombie	B-Application
Panic	I-Application
.	O
</s>
<s>
Set	O
in	O
the	O
middle	O
of	O
a	O
zombie	B-Application
apocalypse	I-Application
,	O
players	O
start	O
as	O
a	O
small	O
group	O
of	O
survivors	O
attempting	O
to	O
stay	O
alive	O
.	O
</s>
<s>
Initially	O
released	O
on	O
December	O
28	O
,	O
2007	O
,	O
via	O
Mod	O
DB	O
page	O
as	O
a	O
public	O
beta	O
(	O
v1.0	O
)	O
and	O
later	O
re-released	O
for	O
Steam	B-Application
via	O
Steamworks	O
on	O
October	O
8	O
,	O
2008	O
,	O
as	O
a	O
free-to-play	O
game	O
.	O
</s>
<s>
Zombie	B-Application
Panic	I-Application
!	I-Application
</s>
<s>
On	O
October	O
8	O
,	O
2008	O
,	O
it	O
was	O
one	O
of	O
the	O
first	O
five	O
"	O
mods	O
"	O
to	O
be	O
released	O
on	O
Steam	B-Application
by	O
Valve	O
under	O
their	O
new	O
commitment	O
to	O
easily	O
accessible	O
quality	O
user-created	O
modifications	O
in	O
the	O
Steam	B-Application
Store	I-Application
.	O
</s>
