[rodw]

The 8-not-10 isn't a problem at all, just a little surprising and maybe a hint that the creator wasn't deeply experienced with sequencers.

To be honest that's fine. I sincerely think this is a pretty elegant implementation, maybe because you're looking at it with fresh eyes.

Traditionally the hardware versions of these things have a pretty clunky and awkward interface that seems designed to minimize the number of switches and dials rather than to be readily understandable. A lot of the "toy" software sequencers you'll find online are clearly modeled on the hardware sequencers - sometimes specific ones - and copy that clunky interface. The "here's a grid, toggle a button to play a sound on that beat" interface is much more intuitive and fun to play with.

I think this is really well done. The only idea for improvement that jumps out at to me would be the ability to drag the cursor with the mouse down to toggle multiple buttons at once rather than independently clicking on each one.