For myself, I’ve used Agilefant (Java), PHProjekt with Scrum Module, Tudu (Java)

I am now using Tracks (Ruby). I really love Tracks– I can export my iCalendar feed, a text feed, and the interface is really easy and powerful.  But, I can’t share my tasks or assign them to other users, there’s no sub tasks (yet), and when multiple items are overdue it floods my Google Calendar on that day. Also, I can’t get it to run through Apache’s fcgi module and have to use mongrel (or thin or event machine).

Other tools I’ve recently looked at, with an emphasis on free and self-installable:

• listingly looks very nice
• WebCollab Great for project management. A little more robust:  dotProject
• chandlerproject Has a desktop app that syncs to a website (hub). The website interface could use more features. A portable build of the desktop app would be great!
• nexty Very nice, I may look into this more.  The multi-user features seem to require me to install it on my server, so I haven’t tested it yet.
• hiveminder
• burdenbutcher
• propelr Not out yet
• todoist
• voo2do
• zirr
• People seem to really like Remember the Milk, (Vista sidebar, Greasemonkey)

List of more:

• Priacta
• GTDTools

Please comment

UPDATE 6/17/09  Zoho Planner looks interesting, as well.  Not really collaborative, but you can invite others to edit it.