Nekoreader is a ‘purist’ feed reader with only three parameters needed to run.
Nekoreader is in all a small API that works on GitHub pages. It has three parameters: feed URLs; template; and style.
The feeds and the template are provided in .json format, and the stylesheet is of course CSS.
It’s easy to share and hack away at, and, of course, you can start off your feed service if you aren’t content with GitHub pages for feed reading.