Tool switching in the Playlist and Piano roll. Single letter keys switch tools with no modifier: P for the Draw tool, C for Slice, D for Delete, E for Select, T for Mute, Z for Zoom. These only work while typing-keyboard-to-piano mode (Ctrl/Cmd+T) is off.
Channel Rack and Step Sequencer. Number keys 0-9 mute or solo the first ten channels directly; Ctrl/Cmd plus a number solos instead of muting. Alt plus the arrow keys reorders channels.
Piano roll note editing. Ctrl/Cmd+Q quantizes the selection, Ctrl/Cmd+U chops notes, and Alt plus a letter opens one of the roll's editing tools (Randomize, Strum, Chop, Arpeggiator, and more).
Transport and playback. Space starts and stops playback, Ctrl/Cmd+Space pauses, and Ctrl/Cmd+M toggles the metronome.