M&M is a playable game. I've run it before. While not running it currently, it's a fun retroclone.
The bit about predating D&D is all spoof. It started out as a gag article, an alternate history of gaming written by Paul Elliot. Ollivier Legrand took the concept, and the description, and turned into a decent RPG. The actual date of release is, according to RPGGeek, 2006. See http://storygame.free.fr/how.html
The actual games, for there are two, are a fun, thin "1972 Mazes and Minotaurs", with a one book core, and the 3 book core "1987 Revised Mazes and Minotaurs".
Both are available from http://storygame.free.fr/
There is no print version. Ollivier has chosen not to put it into a print edition, and the one print edition offered was offered without his consent and was still available despite his Cease & Desist letter...
Several other such "Spoofs" have been released, such as Wanderer (A conversion of Classic Traveller to fantasy), and Dawg (Canine Roleplaying nod to Bunnies and Burrows) but M&M is the only one to have a significant community without a commercial release. Hackmaster 4th Ed is a commercial version derived from AD&D under license.
Just for reference, tho, Dave Arneson notes that the first RPG wasn't D&D, but the Braunstein games, where he went off-board in a minis-game invasion-of-a-banana-republic... back in 1968. He was just a player, but the referee allowed him to do off-map stuff, and he and Gary Gygax then expanded out from there.