Use the tilde (~) key to access a command console. You can then type a command and press enter.
These let you look up internal data, manipulate various aspects of the game, or do other debug-related functions. Some can also be used to cheat.
a_friction (#) Use without a number to check the friction setting, or with one to change it. Smaller numbers mean slipperier movement.
a_gravity (#) Use without a number to check the gravity setting, or with one to change it. Smaller numbers mean weaker gravity; low gravity makes a better jump cheat than the fly command does.
a_jumpheight (#) Use without a number to check the jump height setting, or with one to change it. The default is 800, and 1776 is the maximum safe value before you will jump so high that you die coming back down. It appears not to be just a simple linear scale.
a_moveactor # # # # Move the actor specified by the first number to the position specified by the remaining three numbers.
a_moveme # # # Move the player to the position specified by the three numbers (west-east, north-south, down-up).
a_movemerel # # # This is like a_moveme, but instead of using the true map coordinates, the values given are added to the current ones. Useful for tweaking one's position a little.
dir (name) Print the directory listing of a directory inside the main data file. dir maps is a commonly referenced one for getting the map listing, but other directories like sprites, sounds, and music also exist.
pc_dump # Dump info about an actor on the map. Using 0 as the number will get the player's info and actor number. The player is usually the next-to-last actor (the last being the camera).
pc_runservice (name) Asks for a Service Name as an argument, currently unsure of correct input.
pc_stats Show tallies of some stuff, needs more research.
pc_top Prints some debugging info, might be related to frequently used or most resource intensive game functions?
positions Show the position(s) of players in the game. One use of this is to get positions to move players or other things to with some of the other commands like a_moveme and a_moveactor.
res_fileinfo (name) Display info about a lump in the main data file, invoked by lump name. You can get some of the lump names with dir or res_idlist.
res_idlist Show a listing of lumps that have been loaded from the main data file, with the ID numbers of each lump (which can then be used with res_idstat)
res_idstat # Show info on the specified lump from the main data file.
vp_flatshade (#) Check or set a 0/1 toggle for flat shading. When set, renders the map's static geometry with flat colors instead of texturing them. Could be useful for modders analyzing map structure or checking for geometry problems, or to help understand the map format. Default is 0 (off).
vp_flatshadepolyobj (#) Check or set a 0/1 toggle for polyobject flat shading. Like vp_flatshade but this one is for the map's polyobjects (moving parts like doors and traps). Default is 0 (off).
vp_fov (#) Check or set the field of view setting. Higher numbers means a bigger view but also introduces some vertical distortion. You may also have to use the vp_renderdist command along with it if you want to avoid disappearing geometry on wider views.
vp_printfacedata # Displays some info on the specified face number ("light size" and "plane"). Technical stuff I don't currently understand.
vp_renderdist (#) Check or set the render distance for map polygons. Setting a higher number keeps more distant geometry in view.
vp_rendertorches (#) Check or set a 0/1 toggle for whether the torch flames in levels will be rendered. Default is 1 (on).