Some sources and home of Game Boy Tile Designer (GBTD) and Game Boy Map Builder (GBMB) tools
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A tilemap editor for Game Boy, Color, Advance, DS, and SNES projects. Written in C++ with FLTK.
Flexible and composable tile graphics converter supporting Super Nintendo, Game Boy, Game Boy Color, Game Boy Advance, Mega Drive, Master System, Game Gear, PC Engine and WonderSwan formats.
Gameboy Tile Data Generator
Tilemap GB - Console App - AND - GIMP plugin for importing & exporting Game Boy game tilemaps and tilesets (as bitmap images or .GBM/.GBR files. Related tools: GBTD, GBMB, GBDK, Zal0-ZGB)