With the kind permission of André Michelle, the creator of this (seemingly) simple enjoyment, let me introduce you:
Go and play with this, people!
Addictive, inspiring, fun - and it seems I'm not the only one to think so. Let me try to explain in short and simply, and I do welcome corrections, for the terminology might escape me:
The ToneMatrix is a simple synthesizer+sequencer with which you can create short loops of melodies online.
But here's what caught me: it looks cool. Combined with an effect of a light-wave, it creates a hypnotical, fun interface to play on, which reminds me a bit of Yamaha's Tenori-On. And the ToneMatrix is super easy to play with. Just click on the tiles to light them up and create sounds. Experiment with rhythms and you'll soon be immersed. To save your creation, just right click on the grid and copy.
Once you've had enough play on the Tone Matrix, check out André Michelle's other projects. Whether you want to just play around or are deeper into the algorithms and science behind it all, you'll be sure to find them interesting!