Chandler is a free and open personal organizer being developed by the Open Source Applications Foundation, with design by Andy Hertzfeld of the original MacOS GUI team. Eventually it's meant to integrate email as well as calendaring and to-do items, but for now it's just the latter — that said, the latest release, 0.6, is finally something in shape that's usable by civilians. The Chandler application development arc is a little reminiscent of Mozilla/Firefox: a slow start that lays a solid foundation, with major changes visible at each milestone.
(Thanks, Reid!)
Update: Reid clarifies, "his release, as you might guess from the 0.6 version number, is not a final release. It has been termed 'experimentally usable', and should not be relied upon to keep any data safe. Also, on another note, Andy Hertzfeld hasn't been involved with the project for a couple of years."
