Isocon is a 3d virtual tabletop for tactical combat skirmish/TTRPGs where positioning, elevation, and line of sight matter. With a low learning curve and easy to use tools, you can create 3d terrain about as quickly as you could draw on a battlemat, or spend the time to really set the stage with painting and environmental controls.
Isocon is a labor of love and committed to remaining free to obtain and use.
FOSS: View source code and contribute on Github.
Isocon is licensed under Creative Commons BY-NC-SA.
Game Systems
Isocon supports ICON and Maleghast, but can also be used for generic systems with support for both square and hex grids.
Roadmap
Isocon is still in beta! Features, interface, and game systems are still in flux. There's plenty of work to be done before a 1.0 release.