See also:

• https://github.com/cristoper/feedmixer A self-hosted API to fetch and mix entries from Atom and RSS feeds (returns Atom, RSS, or JSON), written in Python
• https://github.com/makesites/rss-merger Simple PHP aggregator of RSS feerds
• https://github.com/chase-seibert/rsscombine Combine many RSS feeds into one feed, written in Go.
• https://gist.github.com/smajda/204194 Merge multiple RSS feeds with SimplePie, written in PHP.