Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.

Discover on Demand - Just like Spotify's Discover Weekly, but whenever you want.

Anchor CMS - Free and lightweight blogging system

Rocketgraph - Rocketgraph is an open-source drop in replacement to Firebase, except it's much better.

Textpattern - Textpattern is an elegant content management system that is free, open source software.

Spotify - Map shows when two people play same song at same time