iso free web-based project management software

[zimv20]

a friend is the production manager of a small theater company. we're looking for PM software, web-based (many users, decentralized, mac and PC), and free (no $$).

via Fantastico, my websites have immediate access to dotproject and phprojekt, so that's where i'm starting my search.

so far, both look nicely feature-laden and usable. two things they don't seem to have are RSS and webdav. they're not must-haves, but i think it'd be a nice touch.

user experiences for either or both are most welcome.

requirements
---------------
- webserver based
- runs on linux
- free
- can support multiple projects and users
- timeline and gantt charts
- private and shared calendars and contact lists
- robust permissions system
- trouble ticket system

nice to have
--------------
- webdav publishing
- RSS
- nested projects

so -- any packages better than the two i've linked above that i should check into?

also -- i'm not at all well-versed in CMS's. should i be thinking about one of those instead? (and which one?)

thanks!