The user Weasel posted this on the Hardcore Gaming 101 forums and I thought it could be useful for people here too:
"This is a handy little utility that runs in Java (i.e. on any computer) and is primarily designed for mapping out dungeons in tabletop RPG's, but is extremely useful for other stuff too. Basically, the mapping functions in Dungeon Mapper mirror those of the Etrian Odyssey series on Nintendo DS. For my purposes, I've been working with it on the Genesis game Shining in the Darkness and it's worked quite well aside from some graphical glitches that are easily remedied.
https://www.zerker.ca/zzone/2010/01/10/dungeon-mapper-0-1-alphaProbably the best digital equivalent of graphing paper I've seen...ever."