Feed Wrangler
Feed Wrangler is a modern, sustainable RSS reader.
Featuring a web interface, apps for iOS, tight integration with Instapaper or Pocket and ‘Smart Streams’—a clever feature which lets you group selected feeds into a river of news, create feeds based on search criteria, or mute feed items based on keyword filters.
An OS X application is ‘coming soon’, and an API for third party developers is set to launch this month.
A subscription to Feed Wrangler will set you back $18.99 a year; the various apps are free.