Are there open source news aggregators?

Hi! I'm just developing one at http://github.com/msmuenchen/skynetrss (demo instance at http://dtmp.vm-dg.de/rss/ - don't rely on this one working 100% of the time;)).

The only other FOSS project I know about is TinyTinyRSS aka TTRSS.

There are a few still active or not : Gregarius, Lilina, TinTinyRSS, RSSLounge and the more recent selfoss from the same developper. More generally you would search for new informations on the topic with something like "self hosted rss reader" in a search engine

I am working on one: https://github.com/mikejsavage/rssd