I created this tile editor in Unity using the Unity editor API, although you can easily get the same kind of result in any 3D Modeling application, I was looking to create prototyping tool that allow for fast iteration for level design.
By limiting the type of geometry you can create and creating a specialized 3D interface/gizmo for quad/tri based modeling, you gain speed and simplicity at the expense of limiting the type of geometry you can create.
The interesting parts of this implementation is the gizmo that creates geometry, it is context sensitive depending on the type of edge. It is based on the edge direction relative to world space and creates a' gizmo is used to generate new faces.
The other interesting part of this tool was the custom Quad and Triangle UV mapper. It has both a 'Tiled' mode where you can use a grid to click on a tiled texture map and a dragging mode to place individual vertices anywhere on the texture. This tool significantly improves the speed of texturing this type of geometry, as in normal 3D modeling applications we would have to use the standard approach for uv mapping.