Project M is a modification for Super Smash Bros. Brawl made to primarily focus on gameplay of said game's predecessor, Super Smash Bros. Melee, which features the more fast-paced, advanced, and technical gameplay that makes it more competitive as opposed to Brawl's casual gameplay that is compounded by its slowness and its infamous tripping mechanic that occurs at random, its infamy of which is solidified by its ability to disrupt gameplay and open luck-based opportunities for players against those who do trip. As a modification for Brawl, it brings back the cast from that game and gives the newcomers many tweaks that help them fit with the physics of Melee, including some buffs and nerfs (this does not mean all newcomers benefit from said physics), while still keeping the characters balanced amongst one another in terms of their movesets. The mod had become a popular and well-received phenomenon to the point where many tournaments of the mod are held in many places.
Before its cancellation, this mod would receive updates from time to time as an attempt to iron out certain bugs and unfair exploits it possesses, in addition to giving the characters some changes to either buff or nerf them in order to keep the game balanced.
In addition to the cast from Brawl, Project M also brought back two characters that were present from Melee and absent from Brawl, including Mewtwo and Roy, both of which were created with use of the Clone Engine; these characters return with a buffed moveset and newer models.
Development of the mod was discontinued on the first of December 2015, and updates will no longer be released. However, the Dev Build of the mod was shortly leaked after that includes the new characters (Knuckles, Lyn, and Isaac) and alternate costumes (like Roy's Awakening artwork). After that, updates are continuously made in order to fix some bugs that the game still has within it, including instances where certain costumes crash the game when used and models glitch.