libical is an Open Source (MPL/LGPL) implementation of the IETF's iCalendar Calendaring and Scheduling protocols. (RFC 2445, 2446, and 2447). It parses iCal components and provides C/C++/Python/Java APIs for manipulating the component properties, parameters, and subcomponents.
The main page for libical on SourceForge is: http://www.sourceforge.net/projects/freeassociation/
The libical mailing list is hosted at https://sourceforge.net/mail/?group_id=16077
Subversion commits are posted to the mailing list.
Probably you! Practically every non-Microsoft calendar software package in existence includes libical in its build. Here are a few:
You can download libical at Sourceforge.