Proxygen is a great C++ HTTP library.

- fully evented with arbitrary number of threads servicing event loops

- straightforward API with examples

- HTTP 1.1/2/3 out of the box

- terminates SSL/TLS out of the box

- extremely hardened

It’s not tiny and header only or anything trendy like that, but it’s fast as hell, easy to code to, builds with cmake easily, actively developed, and runs one of the biggest sites on the Web.

I have yet to find a major downside.