Clay.app is a 3D n-gon mesh modeler that runs on MacOSX. If you know what Wings3d is about, well Clay.app intends to be that kind of application. It will feature standard mesh operations such as bevel, extrude, bridge, thicken, etc. Smooth meshes are obtained through Catmull-Clark based subdivision. Mesh unfolding and UV mapping will also be implemented. Mesh painting also belongs to the (long) list of planned features. Clay.app results from the development of the Polymesh plugin for the Art of Illusion 3D studio, so it will basically feature the same set of modeling operations.
Clay.app is under development and there is not really enough substance for a preview yet. You'll find some screenshot below that illustrates the work already completed. There is also a 30Mb video in which you can see a 100k face mesh being edited (this mesh is the Ajax head from the Stanford repository remeshed at a lower resolution). Clay.app supports detailed mesh edition as development is currently tested on meshes featuring from 500k to 2M faces.
I'll post snapshots of Clay.app as soon as there will be something to test/try. Until then, feel free to ask questions on the Open Discussion Sourceforge forum.