Various cheats
     Press [~] during the game and type in at the console:

Cheat code:             Effect:
godmode <0 or 1>        Toggle God mode
giveall <0 or 1>        Toggle all weapons with maximum ammo
gui_show_map <0 or 1>   Toggle GUI map
unlimited_ammo <0 or 1> Toggle unlimited ammo
debug <0 or 1>          Toggle debug mode
map drm10               Skip to level  1
map drm10a              Skip to level  2
map drm11               Skip to level  3
map drm12               Skip to level  4
map drm13               Skip to level  5
map drm14               Skip to level  6
map drm15               Skip to level  7
map drm21               Skip to level  8
map drm21a              Skip to level  9
map drm22               Skip to level 10
map drm24               Skip to level 11
map drm25               Skip to level 12
map drm26               Skip to level 13
map drm31               Skip to level 14
map drm31a              Skip to level 15
map drm32               Skip to level 16
map drm33               Skip to level 17
map drm34               Skip to level 18
map drm36               Skip to level 19
map drm37               Skip to level 20
map drm41               Skip to level 21
map drm43               Skip to level 22
map drm44               Skip to level 23