Alternatives to Ultimate Doom Builder

LDtk

LDtk suits game developers designing 2D platformer or top-down levels who want typed entities and tilemap tools.

GtkRadiant

It is aimed at commercial developers and individual modders making levels for supported id Tech games.

GridCraft

GridCraft suits game developers who need to edit tile maps in a browser or desktop app and export to listed game tools.

It suits Windows users making maps for the Source engine who want lighting and visual previews in the editor.

DarkRadiant suits people creating levels and fan missions for The Dark Mod or working with its listed supported games.

NetRadiant suits mappers and game developers building levels for Xonotic, Unvanquished or other supported games.

2D Tiler

It suits game developers who want browser-based tools for maps, tilesets, pixel assets, palettes, and engine exports.

It suits OpenTibia map makers who need terrain, item-search, and map export tools.

Sprite Fusion

It suits 2D game and retro-game developers, people making virtual tabletop maps, and educational app makers.

It suits Mega Man fans who want to build stages, collaborate on them, or play levels made by other users.

Mapster32 suits level designers creating Duke Nukem 3D or related Build-engine maps.

OGMO Editor suits indie game developers who want a free level editor with tile, decal, entity, and metadata layers.

It is aimed at people creating total conversions or editing game resources.

Tiled suits game developers building 2D levels, especially those working with tile maps and terrain.

SonLVL suits people editing level projects for the listed Sonic games, particularly those who need object, chunk, block and collision controls.

TrenchBroom suits mappers creating levels for supported brush-based engines.