<s>
Irssi	B-Protocol
(	O
)	O
is	O
an	O
IRC	B-Protocol
client	B-Protocol
program	I-Protocol
for	O
Linux	B-Application
,	O
FreeBSD	B-Operating_System
,	O
macOS	B-Application
and	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
It	O
was	O
originally	O
written	O
by	O
Timo	O
Sirainen	O
,	O
and	O
released	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
GPL-2.0-or-later	I-License
in	O
January	O
1999	O
.	O
</s>
<s>
Irssi	B-Protocol
is	O
a	O
C	O
programming	O
language-based	O
client	B-Protocol
for	O
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
(	O
IRC	B-Protocol
)	O
,	O
with	O
a	O
text-mode	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
Developed	O
from	O
scratch	O
,	O
it	O
is	O
not	O
based	O
on	O
ircII	B-Protocol
,	O
which	O
allows	O
Irssi	B-Protocol
to	O
have	O
better	O
control	O
over	O
security	O
and	O
customization	O
.	O
</s>
<s>
It	O
supports	O
numerous	O
Perl	B-Language
scripts	B-Language
and	O
plugins	B-Application
for	O
appearance	O
and	O
functionality	O
enhancements	O
,	O
including	O
encryption	O
and	O
other	O
protocols	O
like	O
ICQ	B-Protocol
and	O
XMPP	B-Protocol
.	O
</s>
<s>
Configuration	O
can	O
be	O
done	O
via	O
the	O
user	O
interface	O
or	O
by	O
manually	O
editing	O
configuration	B-Protocol
files	I-Protocol
with	O
Perl-like	O
syntax	B-Application
.	O
</s>
<s>
Primarily	O
designed	O
for	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
Irssi	B-Protocol
is	O
available	O
on	O
various	O
distributions	O
such	O
as	O
Gentoo	B-Application
Linux	I-Application
,	O
Debian	O
,	O
Slackware	B-Application
,	O
SUSE	O
,	O
Fedora	O
,	O
FreeBSD	B-Operating_System
,	O
and	O
more	O
.	O
</s>
<s>
It	O
also	O
runs	O
on	O
Microsoft	B-Application
Windows	I-Application
under	O
Cygwin	B-Language
,	O
and	O
an	O
official	O
standalone	O
build	O
for	O
Windows	O
was	O
released	O
in	O
2006	O
.	O
</s>
<s>
For	O
macOS	B-Application
,	O
text	B-Application
mode	I-Application
ports	O
can	O
be	O
installed	O
via	O
Homebrew	B-Application
,	O
MacPorts	B-Application
,	O
or	O
Fink	B-Application
,	O
and	O
there	O
are	O
graphical	O
clients	O
like	O
IrssiX	O
and	O
MacIrssi	B-Protocol
based	O
on	O
Irssi	B-Protocol
.	O
</s>
<s>
Colloquy	B-Language
,	O
a	O
Cocoa	B-Operating_System
client	B-Protocol
,	O
was	O
once	O
based	O
on	O
Irssi	B-Protocol
but	O
now	O
uses	O
its	O
own	O
IRC	B-Protocol
core	O
implementation	O
.	O
</s>
<s>
Irssi	B-Protocol
is	O
written	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
and	O
in	O
normal	O
operation	O
uses	O
a	O
text-mode	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
According	O
to	O
the	O
developers	O
,	O
Irssi	B-Protocol
was	O
written	O
from	O
scratch	O
,	O
not	O
based	O
on	O
ircII	B-Protocol
(	O
like	O
BitchX	B-Protocol
and	O
epic	O
)	O
.	O
</s>
<s>
Numerous	O
Perl	B-Language
scripts	B-Language
have	O
been	O
made	O
available	O
for	O
Irssi	B-Protocol
to	O
customise	O
how	O
it	O
looks	O
and	O
operates	O
.	O
</s>
<s>
Plugins	B-Application
are	O
available	O
which	O
add	O
encryption	O
and	O
protocols	O
such	O
as	O
ICQ	B-Protocol
and	O
XMPP	B-Protocol
.	O
</s>
<s>
Irssi	B-Protocol
may	O
be	O
configured	O
by	O
using	O
its	O
user	O
interface	O
or	O
by	O
manually	O
editing	O
its	O
configuration	B-Protocol
files	I-Protocol
,	O
which	O
use	O
a	O
syntax	B-Application
resembling	O
Perl	B-Language
data	O
structures	O
.	O
</s>
<s>
Irssi	B-Protocol
was	O
written	O
primarily	O
to	O
run	O
on	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
and	O
binaries	O
and	O
packages	O
are	O
available	O
for	O
Gentoo	B-Application
Linux	I-Application
,	O
Debian	O
,	O
Slackware	B-Application
,	O
SUSE	O
(	O
openSUSE	B-Operating_System
)	O
,	O
Frugalware	O
,	O
Fedora	O
,	O
FreeBSD	B-Operating_System
,	O
OpenBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
DragonFly	B-Application
BSD	I-Application
,	O
Solaris	B-Application
,	O
Arch	O
Linux	B-Application
,	O
Ubuntu	B-Operating_System
,	O
NixOS	O
,	O
and	O
others	O
.	O
</s>
<s>
Irssi	B-Protocol
builds	O
and	O
runs	O
on	O
Microsoft	B-Application
Windows	I-Application
under	O
Cygwin	B-Language
,	O
and	O
in	O
2006	O
,	O
an	O
official	O
Windows	O
standalone	O
build	O
was	O
released	O
.	O
</s>
<s>
For	O
the	O
Unix-based	O
macOS	B-Application
,	O
text	B-Application
mode	I-Application
ports	O
are	O
available	O
from	O
the	O
Homebrew	B-Application
,	O
MacPorts	B-Application
,	O
and	O
Fink	B-Application
package	O
managers	O
,	O
and	O
two	O
graphical	O
clients	O
have	O
been	O
written	O
based	O
on	O
Irssi	B-Protocol
,	O
IrssiX	O
,	O
and	O
MacIrssi	B-Protocol
.	O
</s>
<s>
The	O
Cocoa	B-Operating_System
client	B-Protocol
Colloquy	B-Language
was	O
previously	O
based	O
on	O
Irssi	B-Protocol
,	O
but	O
it	O
now	O
uses	O
its	O
own	O
IRC	B-Protocol
core	O
implementation	O
.	O
</s>
