This is a simple tiled map editor. It's suitable for grid-based game maps, either creating them from scratch or mapping out a game while you play it.
It requires a tileset image. A sample tilset is loaded by default. For something more interesting to try out, try using something from a google image search for "tileset".
To draw tiles, simply drag on the map view. The left and right mouse buttons are each assigned a glyphs, viewable on the right side of the window. Select a tile for either button by clicking one of the glyphs in the gallery on the right, with the corresponding button. The red "X" glyph is an eraser.
You can zoom in and out using the zoom buttons or the mouse wheel, and pan with the middle mouse button or by holding down the Ctrl key.
The maps have layers. Currently only one layer is displayed at a time.
Maps can be saved and loaded in a JSON-based format.
If you want to see it in action with minimal effort, try this tileset and this map. You will need to set the tile size to 16.