OP here. I've been working on an app/platform for people to explore musical ideas. This is a drum machine that a European friend of mine created using the app. You can press the Play button in the top-right corner to start audio playback and customize the pattern being played by clicking the red squares on the step sequencer.
If this example is too big and scary, I've made a simpler drum machine here: https://noisecraft.app/529
And many more examples can be found on the browse page: https://noisecraft.app/browse
One of my all-time favorites is this one: https://noisecraft.app/101
Disclaimer that this is made with laptop/desktop computers in mind and may not work well on mobile. The app supports binding MIDI controls by double clicking on knobs :)