It sounds pretty authentic (well, at least as much as the various ReBirths and 303 softsynths) and flexible (the knobs produce the right amount of variation in the sound), which suggests that there is more to this than a bunch of samples in a simple player. The two options are:
Actually, I spoke too soon; it is, amazingly, one all in interpreted ActionScript. The Java applet merely acts as sound output (for some reason), and isn't even loaded on some machines:
http://lab.andre-michelle.com/fl-909
http://www.flashcodersbrighton.org/wordpress/?p=9
Colour me surprised. Are you sure? I guess AS is bytecode interpreted, and if it isn't too dynamic then that could be reasonably fast. But still, that's a lot of data to process.
Just a quick note that we just rolled out an update of the Hobnox Audiotool. As promised the TR808 is now online, along with two new stompboxes (Compressor and Bitcrusher) and some enhanced functions. Saving is still not possible yet, we’re working hard to make it happen for the next update. More infos here: http://tinyurl.com/68wgvb
Flash, communicating with a Java applet for synthesising sound.