Libical is an Open Source implementation of the iCalendar protocols
and protocol data units.
The iCalendar specification describes how calendar clients can
communicate with calendar servers so users can store their calendar
data and arrange meetings with other users.

Libical implements RFC5545, RFC5546, RFC7529; the CalDav scheduling
extensions in RFC6638; iCalendar extensions in RFC7986; plus the
iCalendar iMIP protocol in RFC6047.