Music Toys?

[KrazyerKate]

Not sure which forum would be more likely to know about this, Gaming or Music, but I'll post here first. I came across Tone Matrix, and I realized that there is an entire avenue of gameplay here that I've never seen explored. I'm a sucker for all sandbox games, but I've only really seen physics toys, and there's plenty of ways of making music fun. Any of you guys got any recommendations for other online music toys?