Development mode is a feature on the user interface that serves both as a debugging tool for developers and as a cheat menu for most other players.
When active, it is seen as an additional menu on the top of the screen.
Items are shown from left to right in picture.
An output log for debugging. Shows errors if they occur, as well as debug outputs.
Allows you to edit game data while the game is running. Currently limited to sound and colonist hairstyles.
Toggles special debug visuals, such as shooting hit chances, infestation chances and toggling fog (fog of war) and snow visibility.
It also allows some debug settings, for example unlimited power, toggling damage, and fast research, learning (i.e. instant boost to lv 20 upon doing a task), ecology, crafting, caravans, etc.
Forces a variety of things to happen. Many things can be done from here; spawning items and pawns, executing events, downing/ killing pawns, there are all done through this menu.
Where some debugging information can be found, like crop economy, item nutrition, and such.
Lets you see what's happening in the game.
Toggles god mode. While active you can build structures instantly at no price and research. Godmode can be also toggled through 'View Settings'.
Godmode persists even when development mode is turned off.
Toggles autopause when an error is logged.
In the Options menu in-game, you have the choice to 'permanently' disable development mode. This prevents you from cheating using this.
You can reset it by accessing the game files.