For a long time I've been a happy user of rss2email, originally written by Aaron Swartz. https://github.com/rss2email/rss2email

It periodically fetches the rss feeds, and sends the content to a specified email address where you can use your email reader to sort them into folders.

Assuming you have a "good" email client, this takes care of most of my RSS requirements: Free software, offline availability, and the ability to read anywhere.

The only missing feature I think it could use is a nice GUI to manage feeds.