The greenlet package is a spin-off of Stackless, a version of CPython that
supports micro-threads called "tasklets". Tasklets run pseudo-concurrently
(typically in a single or a few OS-level threads) and are synchronized with data
exchanges on "channels".

A "greenlet", on the other hand, is a still more primitive notion of
micro-thread with no implicit scheduling; coroutines, in other words. This is
useful when you want to control exactly when your code runs. You can build
custom scheduled micro-threads on top of greenlet; however, it seems that
greenlets are useful on their own as a way to make advanced control flow
structures. For example, we can recreate generators; the difference with
Python's own generators is that our generators can call nested functions and the
nested functions can yield values too. Additionally, you don't need a "yield"
keyword. See the example in tests/test_generator.py.

Greenlets are provided as a C extension module for the regular unmodified
interpreter.

Greenlets are lightweight coroutines for in-process concurrent programming.

Homepage:
https://github.com/python-greenlet/greenlet
