SnappingGecko is a free Grasshopper plugin which provides object snapping features, helping you to keep your definitions clean.

Gerilla for Grasshopper, v0.9, 2013-06-11 Please be advised that Gerilla is still in early development. Gerilla is a plugin for Grasshopper / Rh

Alpaca4D is a FEM solver for parametric structural analysis built on top of OpenSees. Static, Modal and Ground Motion Analysis.