Keyboard shortcuts

Here are key/mouse combinations to perform quickly the most common operations.

(When there are two keys/mouse separated by a + sign, it means that you must hold down the first key, not release it and press the second key or button. Click means pressing a mouse button).

What to do Key
Pick a piece click
Turn a piece (Depending on device availability)
Turn mouse wheel
 ←  or  → 
Touch pad: Touch with two fingers and move
Resize the puzzle  I  (opens the resizing window)
 Ctrl+←  /  Ctrl+→  resizes on the fly
Bring a piece that covers others to back  U  
Nail a piece  Alt+Left click 
Remove the pin of a piece  Alt+Right click 
Hint on a piece  Ctrl+Alt+Left click 
Switch Full Screen mode  F 
View the image  Space 
Solution Frame to position of the image  V  (while the image is visible)
Hide/Show Mini-Image  M 
Show only the pieces of the edge  Ctrl+E 
Show/hide the loupe  Z  or
 Alt +click the desk
Select several pieces (with mouse over the screen or a tray) click + drag
Scatter settings window  R 
Scatter pieces protecting the solution frame (configurable)  Ctrl+R 
Scatter pieces in the whole screen (configurable)  Alt+R 
Save game as (set title, player and password)  Ctrl+S 
Open/close the tray 1  1 
Close all the trays  Q 
Send a piece to the tray 1 (same for 2 to 6)  Alt+1 
Send a piece from a tray to the main desk  Alt+Q 
Open a puzzle from the gallery  enter 
Access the gallery to open a puzzle  Ctrl+O 
Game Info & Options  F2 
Program Options  F3 
Autosolve piece  F5 
Change transparency of ghost image  Ctrl+G 

Almost all these operations can be done through the menus and are shown in them as a reminder.