asyncio

asyncio is the modern module for asynchronous network programming provided with the python stdlib since 3.4. In other words, it's the default stuff at your disposal if you want to code something without waiting on the network.

asyncio replaces the old deprecated asyncore module. It is quite low level, so while you can manually code most network-related things with it, you are still at the level of TCP or UDP. If you want higher-level protocols, like FTP, HTTP or SSH, you have to either code it yourself, or install a third party library or module.

Because asyncio is the default solution, it has a the biggest ecosystem of 3rd party libs, and pretty much everything async strives to be compatible with it directly, or through compatibility layers like anyio.

Twisted

20 years ago, there was no asyncio, there was no async/await, nodejs didn't exist and Python 3 was half a decade away. Yet, it was the .com bubble, everything needed to be connected now. And so was born twisted, the grandfather of all the asynchronous frameworks we have today. Twisted ecosystem grew to include everything, from mail to ssh.

To this day, twisted is still a robust and versatile tool. But you do pay the price of its age. It doesn't follow PEP8 very well, and the design lean on the heavy size.

Tornado

Tornado was developed after Twisted, by FriendFeed, at this weird 2005-2015 web dev period where everything needed to be social web scale. It was like Twisted, but tooted to be faster, and was higher level. Out of the box, the HTTP story is way nicer.

Today, you are unlikely to use Tornado unless you work at Facebook or contribute to jupyter. After all, if you want to make async web things, the default tool is FastAPI in 2023.

gevent

Gevent came about in 2009, the same year as Tornado, but with a fundamentally different design. Instead of attempting to provide an asychronous API, it decided to do black magic. When you use gevent, you call from gevent import monkey; monkey.patch_all() and it changes the underlying mechanism of Python networking, making everything non-blocking.