Cross-posted from the Other Simulation forum, posted here for more exposure (because nobody reads the Other Simulation forum). If the mods feel this shouldn't be here, go ahead and delete.
Website:
4x4beat
Gameplay video (prerelease):
YouTube - 4x4beat - jubeat simulator - beta gameplay
Now, as a disclaimer, I've never played jubeat, so I'm going by YouTube videos and the jubeat website for information. I don't think there's any songs in the actual game with BPM changes or stops, but I'm including them anyways, just in case. The timing, grading, and scoring systems are likely way off from the actual game, but there's not a whole lot I can do about that (I can't find any information on that stuff)
The game is controlled with the 1-9, Q-R, A-F, and Z-V keys, which isn't an ideal solution but there really isn't a better one right now (Windows 7 will support multitouch so if that gets more widespread that would be a better solution)
I wouldn't expect too many massive updates in the future, unless the simfile format is updated. It's really meant more as a "starting block" so (hopefully) more talented and experienced programmers can take up the task of making a better sim.
The sim comes with one simfile (the shitty song in the video), and the website has details about the file format on the sim's website once it's finished.
edit: lol 573rd post, how appropriate