google-rfc-2445 is a Java implementation of RFC 2445 recurrence rules. RFC 2445 describes a scheme for calendar interoperability. This project implements core parts of RFC 2445, including a parser for recurrence rules and date lists and a mechanism for evaluating recurrence rules.
Nomad PIM is an extensible personal information manager. It allows you to keep track of your personal data and provides modules for notes, schedule, contacts, money, diary, and timetracking. It is implemented as an Eclipse RCP application. Like Eclipse, it provides extension points for extensions by additional plugins.