Fan project Dota 2 Auto Chess from Chinese developer Drodo Studio has already attracted over four million users.
The title's Steam Workshop page lists 4,442,984 users at the time of writing, with 364,596 unique visitors to the page. The project rolled out on January 4th, 2019.
Workshop titles do not appear in player tracker sites such as Steam Charts, but over 300,000 users, the title would be the third-most-popular game on Valve's platform right now ahead of Counter-Strike: Global Offensive but behind Dota 2.
That four million total player figure makes the game much more popular than official Dota 2 spinoff Artifact, which launched in November 2018 and - to put it lightly - has failed to take off.
SteamSpy pegs sales between one and two million, which is a massive margin. The game hit an all-time peak of 60,740 concurrent players, which it reached on release, according to Steam Charts. At the time of writing, the game's user peak for the last 30 days is just 2,540, with an average player count of 1,090.
According to a Reddit AMA - translated here - Drodo has been in touch with Valve to discuss Auto Chess' matchmaking system.