Quadrangler is a menu tool that reconstructs the quadrangles from a triangulated polygon object and can optionally reverse a surface subdivision. Both together reduce the polygon count to 1/8 and delivers a clean quad mesh, that can again be edited.
Quadrangler is very fast and delivers a perfect result or no result. It will fail on tri-meshes that are not the result of a triangulation. Quadrangler can be applied to complex object hierachies and multiple object selections.