<s>
EventMachine	B-Protocol
is	O
a	O
software	O
system	O
designed	O
for	O
writing	O
highly	O
scalable	B-Architecture
applications	O
for	O
Ruby	B-Language
.	O
</s>
<s>
It	O
provides	O
event-driven	B-Application
I/O	O
using	O
the	O
reactor	B-Operating_System
pattern	I-Operating_System
.	O
</s>
<s>
EventMachine	B-Protocol
is	O
the	O
most	O
popular	O
library	O
for	O
concurrent	B-Architecture
computing	I-Architecture
in	O
the	O
Ruby	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
EventMachine	B-Protocol
has	O
been	O
used	O
to	O
build	O
a	O
number	O
of	O
different	O
libraries	O
and	O
frameworks	O
in	O
which	O
concurrency	B-Architecture
is	O
a	O
performance	O
concern	O
.	O
</s>
