Old but still popular, ugly but powerful.

Features include: Tile sets; Maps; Layers; Entities (e.g. sprites, power-ups, triggers); Paths (linear and Bezier curves); Mosaics (groups of tiles); Custom variables (for tile sets, maps, layers, entities and paths); DLL-based exporter (you can write your own exporter); Flexible XML exporter (select data to export); A module for loading and drawing a TDX map in Monkey; Flexible binary exporter (select data to export); Binary Map importer; Project files are binary or XML; A software and an OpenGL version.