Artifex Terra 3D, freeware 3D terrain, outdoor scene and world editor based on the Ogre3D engine, output in generic formats. Open source scene loader.
Camoto Studio, an open-source Windows/Linux level, graphics and music editor for a number of early-1990s DOS games
Gamestudio a commercial level editor for the gamestudio engine
Goji Editor Game / app editor and IDE, level / UI layout, code editing and debugging
Grome by Quad Software
GtkRadiant by id Software, Loki Software, Infinity Ward, and Treyarch
Future Pinball - A pinball editor.
QuArK, Quake Army Knife editor, for a variety of engines (such as Quake III Arena, Half-Life, Source engine games, Torque, etc.)
Quiver (level editor), a level editor for the original Quake engine developed solely for the Classic Macintosh Operating System by Scott Kevill, who is also the developer and administrator of GameRanger
SabreCSG a commercial CSG level editor for the Unity game engine
Tile Studio general purpose sprite/level editor for game programmers
ToeTag, a level editor for the original Quake engine, natively developed on and for the Apple OS X operating system
Stencyl includes a Scene Designer module which is used to place tiles, actors, and assign behaviors and settings.
SALTR, web-based, real-time level editor for 2D games that supports tiled, matching, bubble-shooter and 2D canvas based games (runners, arcade and etc.).
Tiled Editor, an open-source tiled map editor.
List of level editors Wikipedia
This is a list of level editors for video games. Level editors allow for the customization and modification of levels within games.