[SPACE] to start and stop. [C] the clear the screen. You can mute [M]usic or [D]rums.
[CLICK] to place flyers. [ALT-CLICK] or [CTRL-CLICK] to remove flyers. [SHIFT-CLICK] to make drums.
[+] and [-] to change the tempo. [ARROW KEYS] to choose the default direction. [<] and [>] to rotate the pattern.

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Idea shamelessly stolen from the awesome Otomata because I wanted to try out Andre Michelle's fantastic Tonfall framework.
You can paste Otomata patterns like this:
Created by @MattRix