Advogato is a site for the free software developer community. It provides the typical weblog-style story postings with follow-up comments, with two twists. The first is that it provides a shared diary/activity log server. The second is that it provides a trust metric which generates a sort of community rating system whereby people achieve a reputation from Apprentice to Master. It's necessary to achieve at least Apprentice certification to post articles but anyone can post diary entries. Discussion sometimes chains between different people's diary entries; this is usually more interesting than the articles. Advogato is a great way to keep up with what other free software hackers are doing.
It's similar to community sites like slashdot and kuro5hin but seems to have a closer-knit community.