For those of you on PC who want to have some fun in single player or LAN, open up the console (which you can enable in options, then open in game with ~). Type in sv_cheats 1 and hit enter. This will enable you to enter in cheats to have some fun. Below are some commands you can then enter in the console and what they do. I have not tried many of these, but I did have fun with the director panic mode and spawning tanks. The last 3 that I bolded can be used for some endless zombie fun
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god 1 - Invincibility
noclip - Enables flying around
nb_blind 1 - Makes the zombies unable to see you (but can still sense you when you touch them).
nb_delete_all - clears all units (zombies and survivors)
z_add - Adds a single infected.
z_spawn bossname - Spawns a boss infected at your crosshairs. Put whatever boss name you wish: tank, boomer, smoker, witch, hunter
give weaponname - Equips you with that weapon
cl_drawhud 0 - So you can't see the HUD
r_drawviewmodel 0 - Makes your weapon invisible
z_common_limit <really big number> - Increases the amount of common infected the director is allowed to use at any given time.
director_panic_forever - Panic events (car alarm, mini-finale) don't end until you reach the safehouse, they just keep coming.
director_force_panic_event - Starts a panic event, as though you had set of the car alarm or something.