MEWER 0.3
The third public test of MEWER is online. This displays the metronome in javascript. There's still some slight drifting with the tempo, but nothing anywhere close to flash. Try it here: MEWER 0.3.
I've also made it a bit harder, although it still doesn't check to see if you've passed the first exercise before giving you the second one. That'll happen in the next major version... as long as the timing works better for people in this version.