Last I checked it was still quite alive with quite a few BBS systems, though admittedly that was a few years ago.

Looks like you can still hook up to it using a Synchronet BBS anyway using the steps available here: https://wiki.synchro.net/howto:fidonet

The homepage for FIDONet itself is here: https://www.fidonet.org/

And the Zone 1 Hub, Dark Realms (a Renegade BBS since 1994) is here: https://www.darkrealms.ca/ It has node lists available if you're looking for systems to connect from.