calcurse is a calendar and scheduling application for the command line. It helps keep track of events, appointments and everyday tasks. A configurable notification system reminds user of upcoming deadlines, the curses based interface can be customized to suit user needs and a very powerful set of command line options can be used to filter and format appointments, making it suitable for use in scripts.
The Daily Journal is a PIM program that is written using Qt. It manages daily notes, appointments, holidays, contact and to-do lists, and issues alerts before scheduled appointments.
Leo is a programmers editor, suitable as IDE, and also provides PIM funtionality. It provides unqiue outlines which are represented in a tree, with view nodes being able to occur multiple times. It's fully scriptable in Python itself, where extensions can access outline data and Leos code directly, export to external files containing outline markup.