Tiled is a general purpose tile map editor. It's built to be easy to use, yet flexible enough to work with varying game engines, whether your game is an RPG, platformer or Breakout clone. Tiled is free software and written in C++, using the Qt application framework.
OGMO Editor is a free, open source, project oriented level editor made for indie game developers by indie game developers. Beyond using Tile Layers to create levels from a tileset, use Decal Layers to freely place, scale, and rotate images to decorate your level, Entity Layers...
Eigengrau's Essential Establishment Generator is a tabletop procedural generation tool for towns, NPCs and much more. It creates paragraphs of text suitable to be read directly to players during a game.
Eigengrau's Generator vs MapForge opinions
It's not even map-making software.
Campaign Cartographer is the leading map making software for games (RPGs, miniatures and wargaming). Campaign Cartographer gives you fingertip control of both the big picture and the small details. Want a large scale map of your adventuring world? A detailed dungeon floorplan?
donjon.bin.sh is a freely accessible, online collection of random generators and other tools for pen-and-paper role-playing games. The collection provides a comprehensive range of advanced generators for creating names, demographics, maps, adventures and even entire worlds.