Vectiler is a terrain and city geometry command-line exporter.
The assets created are under the
It is supported on Linux, mac OSx and Windows platforms.
The source code and documentation are available freely under
the MIT licence on github.
Some example application from Adventures in 3D, a blog post by Nicholas Felton.
Geometry types supported in the exports:
You can find example of model exports done by this tool on my sketchfab account.