NURBS Modeling
Read/write 3DM file; Copy & Paste geometry via clipboard!
http://www.rhino3d.com

3D Mechanical CAD
Read/write 3DM file
http://www.spaceclaim.com

Rapid 3D organic modeling
Read OBJ file (custom primitives)
http://www.cbmodelpro.com/

CB Model Pro allows you to import custom primitives, specified by OBJ files. The mesh in the OBJ file is interpreted by CB Model Pro as the control mesh of a Loop scheme subdivision surface. As a result, there are several restrictions on the OBJ files that may be used as custom primitives:

1. Only triangular faces are allowed (quadrilateral faces will be read and triangulated)
2. The file must be fewer than 100KB in size and have fewer than 1000 faces
3. Every edge should be adjacent to exactly two triangles
4. Every vertex should be adjacent to at least 3 and at most 10 triangles (6 works best)

CAM/CAD with some unique features as well as oddities
Read/write 3DM file (it is not the best implementation of a Rhino I/O toolkit, though)
http://world.alphacam.com/

Generates unfolded patterns from a (low-poly) meshes
Read OBJ file (also LWO, 3DS, binary STL)
http://www.tamasoft.co.jp/pepakura-en/

Flattening a triangle meshes to 2D patterns
Read OBJ, 3DS, STL file
http://www.laminadesign.com/

Converts bitmap to heightfield surface
Write IGES file
Download link (zip 0.5 MB)

Program which creates a relief type surface from an input bitmap, where height is controlled by the brightness of the image.

MoI forum ¦ Czech article ¦ Info in English (pdf)