I've been using Python's Tornado (http://www.tornadoweb.org/ http://www.tornadoweb.org/) for years now. Now on version 6, it's fast, well maintained, mature, a

I've been using Python's Tornado (http://www.tornadoweb.org/ http://www.tornadoweb.org/) for years now. Now on version 6, it's fast, well maintained, mature, and has good docs with readable code. @bdarnell has done an excellent job maintaining it. Here's one example: Tornado supported async style coroutines before asyncio was a thing. Now it uses asyncio under the hood by default -- and it did so with an exceptionally smooth transition.