This one is in 3D!
Use keys 0-9 to select material (voxel type) and up/down arrows to change y slice of the map. Use mouse button to place/remove voxels. This applies only in the "change voxels" mode.
Meshing generates a mesh without faces that are completely covered with voxels. For simplicity, faces that have at least one air voxel touching them are not removed. This makes it unsuitable for transparent voxels, but it generates a mesh with fewer polygons.