RSSme - RSSme is free, lightweight and user-friendly RSS editor.
calibre - Ebook manager, viewer & converter
Feed Launch .NET - Feed Launch .NET is an open-source feed editor for RSS 2.0 and ATOM 1.0 Feeds.
FBReader - FBReader is an e-book reader for various platforms. Features:
Feeder by Reinvented Software - Feeder is for creating, editing and publishing RSS feeds on macOS.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.