"Implementations" is a tool to track software applications and the "features" they implement (intended mostly for protocol support, but any kind of feature works), displayed as matrix.

It is intended for email, but the tool isn't specific to email and would work for other kinds of software/protocols.

See:

https://implementations.modernemail.org/

Anyone can make changes, please be thoughtful about adding features/software. See the "About" page on the URL above for more information.