<s>
ical	B-Operating_System
is	O
a	O
calendar	B-Operating_System
package	O
written	O
in	O
Tcl/Tk	B-Application
by	O
Sanjay	O
Ghemawat	O
for	O
Unix	B-Application
systems	I-Application
.	O
</s>
<s>
ical	B-Operating_System
is	O
known	O
for	O
its	O
simple	O
,	O
intuitive	O
interface	O
.	O
</s>
<s>
It	O
's	O
possible	O
for	O
Tcl/Tk	B-Application
programmers	O
to	O
extend	O
ical	B-Operating_System
with	O
custom	O
functionality	O
.	O
</s>
<s>
ical	B-Operating_System
is	O
free	B-Application
software	I-Application
released	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
ical	B-Operating_System
is	O
not	O
related	O
to	O
the	O
iCalendar	O
format	O
standard	O
,	O
and	O
does	O
not	O
support	O
it	O
.	O
</s>
<s>
It	O
is	O
also	O
not	O
related	O
to	O
Apple	O
Inc.	O
'	O
s	O
calendaring	O
application	O
,	O
Calendar	B-Operating_System
(	O
which	O
was	O
previously	O
called	O
iCal	B-Operating_System
)	O
.	O
</s>
