ASE (Allegro Sprite Editor) is a program specially designed with facilities to create animated sprites that can be used in some video game. This program let you create from static images, to characters with movement, textures, patterns, backgrounds, logos, color palettes, and any other thing that you think.
apoplexy is a level editor for Prince of Persia 1.
A wad composer for Doom, Heretic, Hexen and Strife. It can be used to extract the lumps of a wad and save them as individual files. Conversely, it can also build a wad from separate files.
eme is a framework for building a map editor. It uses the Allegro game library and features multiple layers, undo, uses allegro datafiles and random fill.
Final Fantasy VI Save State Editor
ff6edit is a program that can be used to edit the save state information in Final Fantasy VI (or FFIII in the USA) in order to customize your characters however you see fit. It will be written in C++ and run in the GTK environment.
Flexlay is a generic 2d editor, with focus on games. It currently supports multi layered tile- and object maps, full undo/redo, support for tile-brushes, easy copy/paste, multiple buffers, minimap support, a metadata editor, drawing/sketch layers and some other stuff usefull for creating levels for 2d games. Flexlay uses ClanLib and Ruby.
FlightGear Scenery Designer
FGSD is an OpenSource interactive program that allow its user to design custom sceneries for the FlightGear flight simulator project. The basic idea is to use scan of commercial maps and other bitmap data to help users to draw features on top of the image layer. Features includes static 3D objects (buildings for instance), height (hypso) curves, land use contours, roads, railways and powerlines, water area or streams.
GiMd2Viewer is a Quake 2 model viewer (.md2 files). It will be a Gimp plug-in, so that skin artists will be able to test their jobs without leaving 'The Gimp'.
GtkRadiant supports "vanilla" Quake III Arena editing and Quake III: Team Arena.
Hackers lets you manage a set of character databases for NetHack.
Kartta is an isometric tile map editor. It supports both diamond and staggered maps with multiple levels and multiple tile layers. XML is used for data files. Requires gtkmm and boost libraries to build.
Neveredit aims to provide end-user module editing facilities for Bioware's Neverwinter Nights computer game. It used to be a wxWindows GUI on top of libnw, another OpenKnights project.
pu6e is a world editor for Ultima 6 and the Worlds of Ultima (Martian Dreams and Savage Empire). It's written in Python and uses wxWindows and OpenGL. pu6e is tested on Linux and Windows 2000, and requires a 3D card.
PyCraft is an offline world editor for Minecraft, the multiplayer sandbox game.
Quest is a fully featured and widely used DOS-based quake level editor designed. This is the official side of the ported version of Quest to Linux and Unix in general.
SparkEdit is a 3D scene editor that should help you to create a 3rd person role-playing game.
Tegel Tilemap Editor
"Tegel" is an add-on for Allegro for drawing and handling layered tilemaps. The package contains an editor and a playback library in C. There is support for multiple layers and rotated and/or animated tilemaps. The editor is easy to use, with unlimited undo, copy/paste, flood fill, and help included.
tileFoundry is an isometric map editor that is being developed for a game. It reads and writes XML files, uses PNGs for tiles, and has been developed with a focus on ease of use.
Yadex is a Doom level (wad) editor for Unix systems running X, including Linux. It supports Doom alpha, Doom beta, Doom, Ultimate Doom, Final Doom, Doom II, Heretic and also, in a more or less limited way, Hexen and Strife. It is available under the terms of the GPL.