Ask HN: Interesting APIs

I'm looking for interesting WebSocket and REST APIs to build hobby projects. I've checked the resources on https://github.com/public-apis/public-apis, but I'm specifically interested in suggestions beyond what's listed there.

The last Ask HN post is a couple of years old[0]. Any suggestions would be greatly appreciated.

[0]: https://news.ycombinator.com/item?id=25566620