Pure java implementation of the entire Collaboration Data Objects (CDO 1.21) library for accessing Microsoft Exchange Server in a platform independent manner. Subsequently, support for directly accessing Exchange (without CDO or MAPI) will also be added.
OmniObject is a free replacement for Microsoft DCOM, with some advantages: more configurable, Internet friendly and open source (thus you can debug it). We're now Windows only, but we have plans to support *nix soon.