Moonmoon is a web based aggregator similar to planetplanet. It can be used to blend articles from different blogs with same interests into a single page.
Moonmoon is stupidly simple: it only aggregates feeds and spits them out in one single page. It does not archive articles, it does not do comments nor votes.
Web hosting with 5 (PHP4 will not work).
Moonmoon is free software and is released under BSD license.