An online, multiuser, networked, graphical, interactive, programmable virtual tabletop.
MapTool is much more than just a mapping program. Included are not only powerful tools for the creation of detailed maps, but also a chat function, detailed token management (allowing you to track properties of the units placed on the map and display health and status information), and an initiative tracker. Functions not being used can be hidden out of sight. These features enable your computer screen to function as a virtual table top, filling the role of battlemats and dry-erase markers and providing for infinitely scrollable maps and the ability to use a large-screen TV or video projector. It is "game system agnostic", meaning that while MapTool has special support for some game systems (like hexes for GURPS or square templates for D&D 4E) there is no requirement for you to use these features.