One of my favorite little open-source applications has always been activeCollab, which was originally started as an open-source version of BaseCamp, the venerable project management tool from 37Signals.
I have used activeCollab for myself off and on, and I also recommended and installed it on my server for the UGA Quiz Bowl team. It is a nice little application.
Recently, the developer behind activeCollab decided to make the upcoming release closed-source and will charge for the software, despite promises of a free-edition (there will no longer be free version).
I figured that sooner or later someone would fork the last open-source release of activeCollab (version 0.7.1) and begin work on their own version of activeCollab. And it has been done!
ProjectPier is the name of the new open-source collaboration software that used to be activeCollab. As far as I can tell, ProjectPier was started in July, and they recently presented their first release (version 0.8) to the community.
Right now ProjectPier is basically the old version of activeCollab with new branding and a couple of bug-fixes. The developers are open to integrating any ideas the community likes, so let them know what you are looking for.
ProjectPier is also already getting press in the blogosphere, and I believe much more will be coming because of activeCollab closing its source.