As announced recently, activeCollab is no longer free. They have adopted the familiar model - like SugarCRM and many others - where there are multiple versions of the software. At this point, there seems to be a "Lite" (open source) and a "Pro" (commercial) version.

While I don't know the internals of their project, what led to this decision, or how this will impact development, I understand that many in their community are upset... activeCollab originally billed themselves as the free alternative to Basecamp and it appears this is no longer the case.