Serious Sam II

Press tilde and drop the console. Enter sam_iEnableCheats=1 to enable regular cheats. Enter sam_iEnableCheats=2 to enable developer cheats. (Unverified)

On the game's main menu, hold LEFT SHIFT and input F3, F4, F3, F3, F4. Press F1 to drop the cheat menu. (Unverified).