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 PHP5 (PHP4 will not work).
Moonmoon is free software and is released under BSD license.