nextzen and mapzen DEM tiles to generate 3d meshes. The assets created are under the
.obj format. It is supported on Linux, macOS and Windows platforms. The source code and documentation are available freely under the MIT licence on github.
Consider using its fully integrated user interface at halfmaps.io; its successor with more advanced capabilities and ease of use.
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.