Rated 5 out of 5 stars

https://github.com/thsmi/sieve/
Several years ago Mozilla made a strange decision. They dropped their very flexible addon system and copied the extremely limited WebExtensions from Google Chrome. An this ultimately meant for Thunderbird that "classic" addons will go way.

Now in 2020 classic Thunderbird addons are dead. Which meant for the addon it needed to evolve and drop its Thunderbird dependencies. It is now a portable standalone application!

This review is for a previous version of the add-on (0.3.1).  This user has a previous review of this add-on.