The in-game console can be useful in many ways. It can be opened by pressing Shift + Esc. Here are some of the most useful commands:

/devmap = enables cheats in the given map name

/map_restart = restarts the map

/mEnable Instagib = enables Instagib ( 1.2 only )

/give_all = gives the player all weapons

/give health = instantly heals player to 100% HP

/god = enables god mode (makes player invinsible)

/give = combine with the name of any powerup or weapon

/noclip = allows the ability to go through walls

/kill = instantly kills the player (useful when getting stuck somewhere)

Tip: To quickly repeat any of these commands (for example /give), simple press the up arrow while still in the console and then enter. Keep spamming it until your heart's content.