Commune is a project to consolidate various Useful services in a nice package for easy hosting by the resident "computer guy". More info at http://www.33bits.eu/txt/commune.txt.
Any number of webmail/SMTP/IMAP providers with proper security/anti-spam features (e.g. smart greylisting). Maybe a simple mailing list server as well?
CalDAV-capable, with nice UI and sharing/importing features.
- apt-cache search caldav ..?
Fairly restrictive within the group.
- Subsonic has a good start, specifically the Madsonic mod.
Make/use a nice library for providing Persona.