Key commands

General

Alt+F4 Exit
Ctrl+N Create new file
Ctrl+O Open file
Ctrl+S Save file
Ctrl+E Export file
F1 Help
F2 Move focus to pattern editor
F3 Move focus to frame editor
Return Play song / stop
Shift+Return Play pattern looped
Ctrl+Return Play a single row
F5 Play from start of song
F7 Play from start of cursor
F8 Stop playing
F2 - F9 Select octave 0 - 7, if no other keys are configured.
F12 Kill sound
Alt+F9 Mute channel
Alt+F10 Solo channel

Editing

Ctrl+X Cut
Ctrl+C Copy
Ctrl+V Paste
Ctrl+B Paste and overwrite
Ctrl+Z Undo last action
Ctrl+Y Redo last action
Del Delete selection / selected row
Backspace Delete the row above
Ctrl+G Interpolate
Ctrl+R Reverse
Ctrl+F1 Transpose notes one step lower
Ctrl+F2 Transpose notes one step higher
Ctrl+F3 Transpose notes one octave lower
Ctrl+F4 Transpose notes one octave higher
Space Switch between edit / normal mode
Ctrl+Right Go one frame forward
Ctrl+Left Go one frame backward
Tab / Alt+Left Go to to next channel
Shift+Tab / Alt+Right Go to to previous channel
+ Next pattern
- Previous pattern
Numpad 0-9 Select instrument 0 - 9
Alt+Numpad 0-9 Set step size, 0 - 9
/ Select previous octave
* Select next octave
Ctrl+Up Next instrument
Ctrl+Down Previous instrument
Alt+I Edit instrument 

These are the default shortcuts, some are customizable from the configuration window.