This was posted back in June to the sticky list of mapping software but I recently got pointed back to it by NathanaŽl Terrien's post on G+.
Pyromancers' Dungeon Painter is an on-line tool for building maps.
From Randy's post:
I played a bit with it and it seems a nice alternative to some of the older tile based mapping tools (Dungeon Crafter, Dungeon Forge, etc.) with some advanced tools like polygons and elliptical shapes as well.Quote:
Free online mapping software.
Plenty of textures and objects,
layers and groups,
export to images and PDF,
hex and square grid,
simple file format, etc.
The wall builder seems a bit week, but functional.
It also supports layers, and can export as multi-page pdf files.
If anyone else has experience with this tool, I'd appreciate feedback here.