- Miniflux, an opiniated feed reader with Fever API support (writen in Go, uses Postgres as backend)
- Page2RSS, a service to track web page changes.
- RSSOwl, a Java-based aggregator.
- Raggle, a Ruby-based CLI aggregator.
- RSS Merge (uses LastRSS)
- Planet, a flexible aggregator that powers a number of sites.
- Hep - a very nice Twisted Python aggregator with a POP3/IMAP interface.
- FeedBurner - slices and dices feeds (also converts between RSS and Atom). I expect it to start adding advertisements somewhere along the line.
- rss2mail - Perl implementation
- Mimir, RSS feeds via IM using Jabber
- Tapestry - Comics via RSS
- RSS Autodiscovery using PHP
- nntp://rss (read RSS feeds with a News client. Neat.)
- RSS Display (a Perl CGI)
- Ultra-Liberal RSS Parser
- XSLT blogroll for MovableType
- Onyx RSS Parser - a PHP parser
- RSS to IM Gateway
- A Python Bayesian Classifier called Reverend that might well be useful for rating RSS feeds
- Magpie, a PHP RSS parser
- Atom and RSS Feed Library for PHP
- Mailfeed - a PHP script that generates an RSS feed off a POP3 or IMAP mailbox.
- RSS and you (XML::RSS and friends)