A destructively challenging 7-keys-and-turntable game. It is much harder to learn than DDR. However, the game series only came out in Japan, and an arcade cabinet would cost many thousand dollars to import to the U.S. Sunnyvale Golfland (SVGL) is a location known to have this very rare game.
The upside to it not being very well-known unlike DDR is that most of the players are skilled at it, and don't whore the same song 8476385734985 times in a row like DDR players do.
A nearby 15-year-old IIDX player strangled a 12-year-old dumbass DDR player for playing and failing song "Afronova" 25 times in 5 consecutive games.
Meanwhile, at the nearby IIDX machine, no song was played more than once every 5 songs, and a lot of players were seen with scores upwards of 180,000 out of a possible 204,620 points on "flashing 7" songs.
See Beatmania IIDX.
Let's go play IIDX, ya?