A truly unique and incredibly polished sequencer. It really makes me want to see it used live by a musician.
I wonder about the interface: I think it’s maybe a shame to have actions that can only be done with the keyboard. Keyboard shortcuts are for sure the right way to use goosegrid. But in some situations it’s always good to have an alternative way to do actions. In my opinion there could be more buttons, for entering notes there could be for example a mini keyboard. You can always offer the user to hide these toolbars if they want to keep it minimalistic. The other interest would be to help user to learn how to use the tool. When you get to a new tool it’s easier to explore and test things with the mouse than to try random keyboard shortcuts, if the shortcut for each command is displayed on hover, you can gradually learn to use the tool more efficiently.