Project M is a popular modification for the third entry in the Super Smash Bros. series, Super Smash Bros. Brawl, and currently has over 1 million downloads. It is currently on Version 3.6.
Designed to play like its predecessor, Super Smash Bros. Melee, Project M features not only the playable cast of Brawl, but also Mewtwo and Roy, two cut fan-favorites from Melee. It also includes more neutral stages, new alt costumes, improved AI, advanced techniques, momentum physics, and wavedashing, which is a faster (albeit more difficult) way to move on the ground.
Before the reveal and subsequent release of Super Smash Bros. for Nnitendo 3DS/Wii U, Project M became extremely popular in competitive Smash, almost surpassing Melee. Many famous Smash players (such as Hungrybox, Mew2King, and Leffen), who are occasionally mentioned on Miiverse, play it at competitions, which also helped it grow in popularity. Among other things, it predicted certain changes that would be made in 3DS/Wii U, such as Charizard becoming his own character, Mewtwo's confusion being a true reflector, and the buffing/nerfing of several characters, such as Jigglypuff and Meta Knight. It was featured in major tournaments like Apex 2014.
Since the release of Super Smash Bros. for Nintendo 3DS/Wii U, Nintendo has been more active to the competitive scene, sponsoring many major tourneys. Because of this, tournament hosts sponsored by Nintendo don't host Project M competitions. PM was also removed from the Twitch directory. Even though it has lost a large chunk of it's popularity, the Project M Development team still developed new versions until December 1st 2015, when they announced they would no longer continue to develop Project M and removed all PM downloads from the site.
On December 1st, 2015, Project M officially ceased development. It is unknown whether or not Nintendo was the cause of this, but the PMBR claimed it was to work on new, original projects and to avoid potential future legal actions. Several new costumes that were announced for a future version, as well as 4 original characters that were leaked (Knuckles, Lyn, Isaac, and Sami from Advance Wars), influenced another team to pick up the PMDT's dropped work.
Mentioning Project M on Miiverse is forbidden, and while not specifically mentioned in the Code of Conduct most posts mentioning Project M are removed for "criminal activity". This is likely due to its nature as a mod, which Nintendo discourages on its hardware. This has occasionally led to confusion with the game Metroid: Other M's developer, which also goes by the name 'Project M'. Even saying "PM" could possibly get you an Admin Notification.