Here We Go Round the (Open) Mulberry Bush
Mulberry started off life as a software project that was really meant to help the author learn more about the internet and internet protocols used for email. However, it became much more than that and garnered support from a small (in internet terms) group of users and institutions many of whom relied on the product as their primary email tool.
Whilst it started as only an IMAP client and only on Mac OS, it has grown to cover not only other email protocols, but also calendaring and scheduling and is available on Mac OS X, Windows and Linux systems.
Not something I use myself, but good to see it going open source, not least because calendaring and scheduling is an area where free software offerings are still rather thin on the ground:The full code for Mulberry (Mac OS X, Windows and Linux) is now available as open source under an Apache 2 License. Full details available on the wiki.
(Via heise online.)