Campaign Cartographer - Campaign Cartographer is the leading map making software for games (RPGs, miniatures and wargaming).
PyMapper - Drag and drop tile based mapping program.
Mipui - An online grid-based map editor for games, with real-time collaboration.
Dungeon Tile Mapper - Dungeon Tile Mapper is a web based tile mapping tool that includes many official D&D tile sets.
donjon.bin.sh - Freely accessible online collection of random generators for tabletop games.
Fractal Mapper - With Fractal Mapper, creating worlds has never been so easy!