New version for rhino 5 here Auxpecker is an easy and free solution to get a pleasing realtime preview of objects directly on the viewport of Rhino

Stella3D is a plugin developed by Erfan Rezae & Salar Anahid, which simulates the behavior of the particles in a customizable environment.

With this you can make many high quality G2 fillets at the same time with the same chord length.

Fenix is a full-featured elastic finite element analysis and structural design plug-in for Grasshopper.