I have designed a tileset that contains every possible tile that can be used in a game. The result contained 48 tiles. I have done a little expansion for alternate tiles and now it has 64 tiles layed on an 8x8 grid.

Tileset.xcf contains mask and shading as well as a simple example.

Tileset-test.xcf is the file that is used in the preview. However, this file is not covered under this license, its just a sample. Grass texture is used from here and marble texture is from GIMP's own textures (I cannot find any exact license thus assuming its GPL [though it shouldn't be]).

Shading might have problems, if you see one please report so that I can fix it.