Shameless plug for my book on the history of phone phreaking: "Exploding The Phone: The Untold Story of the Teenagers and Outlaws Who Hacked Ma Bell". Plus tons of original research documents here: http://explodingthephone.com/
Project MF is super cool. I didn't know they were still around and doing stuff, but hey, there are updates on that site from after 2020.
A lot of MF signaling stuff has actually been merged into mainline Asterisk nowadays: https://wiki.asterisk.org/wiki/display/AST/Asterisk+19+Appli... With some dialplan work, I've used it to set up my own blue-boxable system without any project MF patches at all - which is handy since the site does say the patches only run on very old versions of Asterisk.
As for why it's merged into mainline, you can thank the Phreaknet guys: https://portal.phreaknet.org/ They run a whole network of simulated MF and SF-controlled switches with Asterisk. It's pretty sick.
Super cool. I've been wondering if something like this existed since I started listening to Evan Doorbell's Telephone Tapes that got posted a few weeks ago (http://www.evan-doorbell.com/production/group1.htm).
A blog post related to Project MF from, gosh, 15 years ago: https://blog.historyofphonephreaking.org/2008/07/business-ca...