Switch between fullscreen and windowed mode:
Press 'F12' key

Pause the game:
Press 'P' key

Move camera to current hedgehog:
Press 'H' key

Make a screenshot:
Press 'C' key

Switch weapon:
Press 'F1'-'F9' keys, or use menu, accessible via right mouse button click

Switch between hedgehogs:
Select the "Switch Hedgehog" weapon and "fire" it by pressing spacebar once.
Press tab to switch between different hedgehogs until you find the one you want.

Sound volume up/down:
'0' key is for volume up, and '9' key is for volume down

Aim precisely:
Press left shift key

Set grenade timer:
Press '1'-'5' keys

Control the direction of Air Attack:
Press 'left arrow' or 'right arrow' key

Construct different girders:
Press 'left arrow' or 'right arrow' key when using construction tool

Speed up demo playing:
Press 'S' key

Enter chat message:
Press 'T' key

Enter chat message (that will send only to my allies):
Press 'Y' key