Nice work! If it will support ASCII export I may stash one of my side projects forever :)

Minor feedback: not all buttons seem to be accessible to keyboard-only users. I'm just a Vim snob with a browser plugin, but for people who actually can't use a mouse your app seems like it would be perfect for them if you fixed that.

Edit: just making the "shortcuts" button accessible may be sufficient, as that shows how to use the keyboard shortcuts.