This looks useful as a starting place for thinking about proprietary community platforms. Also check out Sift of course! There’s a bigger analysis of using open source software for online communities by IBM, undertaken in 2006, here. There’s also a fun-looking forum on the subject hosted by IBM, though perhaps a tad too techi for me.
My colleague Jeremiah Owyang has spent a whole lot of time in the last 4+ months looking at Community Software platforms from companies like Telligent Systems, Jive Software, Pluck, and Mzinga. The full report is available to Forrester clients or you can pay for it separately.
You can get a lot more detail on Jeremiah’s blog post. He’s going to be one busy boy helping companies make these choices, now that the Wave is out.