GridMapper is an application for Windows that allows you to rapidly develop dungeon and building complexes. You start with a filled-in underground map, and from the first click you're clearing spaces for dungeon rooms, corridors, etc. Additional options under "Tools" allow you to easily place doors, stairs, and walls. Save, open, print, resize, and copy your map to other image-manipulation software. It's easy!
DOWNLOAD NOW (GridMapper.exe for Windows; 64KB)
Also, the full source code to GridMapper is released under the GPL v2. VC++ 6.0 workspace included.
Download Source Code (GridMapperV1-0.zip; 26KB)
If you like GridMapper, consider donating (suggested $5 or $10). Thanks!