YouTube - 4x4beat - jubeat simulator - beta gameplay
It's nearly finished, I just need to make an icon, and a few tweaks to the simfile format to allow for BPM changes that aren't whole numbers, and stops. The public release should be out in a few days.
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)
Once the sim is finished, I wouldn't expect too many massive updates, 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 will come with one simfile (the shitty song in the video), and I'll put details about the file format on the sim's website once it's finished.