Dave's Mapper

Allows you to generate geomorphic role-playing maps from a series of expertly crafted tiles by a wide variety of fantasy cartographers. There are a variety of supported map types, generation modes, and styles to choose from. The app supports PNG export in many of the generator modes, as well as viewing on-screen. New tiles are added frequently, and users with mapping experience are encouraged to contribute tiles. Features and updates are also added routinely.

Screenshots from Chrome Web Store