Serious Sam 2
At the main menu, hold [Left Shift]. Press [F3] [F4] [F3] [F3] [F4]. Then, press [F1] to access the cheat menu.
Cheat Mode (Demo version):
Press ~ during gameplay to display the console window. Type sam_iEnableCheats=1 to enable cheat mode. Press ~ again, then press [Esc] to access the main menu. Press [F1] to access the cheat menu..
Thanks to Revolution reader tundrajumper, ns10tree!