On Android I am using Flym, though it doesn't seem to get old entries upon subscription. It is built on the sparse rss app, it is GPLv3 and it has a newer relative spaRSS https://github.com/Etuldan/spaRSS which is more recently maintained.
Thanks for bringing that to my attention! spaRSS is a decent contender. It's pretty, fast and it looks like it does what it should. One small wrinkle: it doesn't seem capable of importing opml files on newer android devices. A bug was filed 2 years ago, but it was closed without being fixed.
