Tiled
Flexible level editor
...Tiled's map format (TMX) is easy to understand and allows multiple tilesets to be used in any map. Tilesets can be modified at any time. Tiled is a general purpose tile map editor for all tile-based games, such as RPGs, platformers or Breakout clones. Tiled was originally written in Java. In 2008, work began to develop a faster, better looking, and easier-to-use version of Tiled based on the Qt framework. This decision was made as the Qt framework has a greater feature set than is offered by the standard Java libraries. Before you can compile Tiled, you must ensure the Qt (>= 5.6) development libraries have been installed as well as the Qbs build tool.