Designed for MapTool, probably compatible with most other VTT systems, and certainly compatible with GIMP/Photoshop if necessary.
A tileset of just walls; use your own textures and props to make whatever background you want, and then lay these overtop to create shaded, complex dungeons, buildings, and caverns of your own devising.
Each tile is a 500x500px transparent PNG. Every one can be rotated or flipped and still line up with few to no visible artifacts. Use any repeating texture or drawings underneath!