Fraidycat is a desktop app or browser extension for Firefox or Chrome. Use it to follow people (hundreds) on whatever platform they choose - Twitter, a blog, YouTube, even on a public TiddlyWiki. Available as a browser extension for Firefox and Chrome (works with Vivaldi too) and as an app for Windows, macOS, and Debian/Ubuntu Linux. Free, open source.
It can monitor RSS feeds and alert you for new posts, but it can also monitor some nonRSS sites like Twitter, Instagram, SoundCloud plus Pinboard, Reddit, Youtube and Tiddlywiki.