<s>
Gem	B-Application
Tower	I-Application
Defense	I-Application
is	O
a	O
tower	B-Application
defense	I-Application
video	O
game	O
created	O
by	O
Bryan	O
K	O
.	O
It	O
was	O
released	O
on	O
February	O
18	O
,	O
2007	O
,	O
under	O
the	O
tower	B-Application
defense	I-Application
subsection	O
of	O
Blizzard	O
's	O
Warcraft	B-Application
III	I-Application
:	I-Application
The	I-Application
Frozen	I-Application
Throne	I-Application
minigames	O
.	O
</s>
<s>
Several	O
game	B-Protocol
clients	I-Protocol
,	O
Flash	B-Operating_System
browser	B-Protocol
game	I-Protocol
websites	I-Protocol
and	O
mobile	O
devices	O
have	O
hosted	O
variants	O
of	O
the	O
game	O
.	O
</s>
<s>
The	O
first	O
Gem	B-Application
Tower	I-Application
Defense	I-Application
sprung	O
from	O
Blizzard	O
's	O
Warcraft	O
game	B-Protocol
client	I-Protocol
under	O
the	O
name	O
 [ BK's ] 	O
Gem	B-Application
TD	I-Application
v1.4	O
featuring	O
42	O
levels	O
,	O
unique	O
combinable	O
buildings	O
,	O
multiplayer	O
gameplay	O
and	O
an	O
open	O
map	O
for	O
players	O
to	O
explore	O
.	O
</s>
<s>
Under	O
the	O
"	O
Tower	B-Application
Defense	I-Application
"	O
genre	O
,	O
it	O
is	O
also	O
known	O
as	O
Gem	B-Application
TD	I-Application
.	O
</s>
<s>
The	O
concept	O
diversified	O
into	O
a	O
flash	B-Operating_System
adaption/imitation	O
producing	O
a	O
browser	O
playable	O
variant	O
.	O
</s>
<s>
Multiple	O
replication	O
of	O
the	O
game	O
have	O
popped	O
out	O
from	O
minigame	O
supported	O
multiplayer	O
games	O
and	O
devices	O
such	O
as	O
Dota	B-Application
2	I-Application
Reborn	O
,	O
Blizzard	O
's	O
StarCraft	O
II	O
,	O
Windows	O
and	O
iOS	O
.	O
</s>
<s>
Gem	B-Application
Tower	I-Application
Defense	I-Application
is	O
a	O
tower	B-Application
defense	I-Application
game	I-Application
built	O
on	O
planning	O
and	O
chance	O
.	O
</s>
<s>
The	O
concept	O
of	O
Gem	B-Application
Tower	I-Application
Defense	I-Application
is	O
to	O
efficiently	O
use	O
mazes	O
,	O
Gems	O
,	O
and	O
planning	O
to	O
win	O
the	O
game	O
.	O
</s>
<s>
Gem	B-Application
Tower	I-Application
Defense	I-Application
employs	O
the	O
use	O
of	O
eight	O
basic	O
Gems	O
:	O
</s>
<s>
All	O
the	O
units	O
in	O
the	O
same	O
wave	O
will	O
have	O
identical	O
details	O
based	O
upon	O
the	O
tower	B-Application
defense	I-Application
norms	O
:	O
</s>
