Ayam is described as 'free 3D modelling environment for the RenderMan interface, distributed under the BSD licence. This means that neither the author nor any contributors make money out of this software' and is an app in the Photos & Graphics category. There are four alternatives to Ayam for Mac, Windows and Linux. The best alternative is Rhinoceros. Other great apps like Ayam are MODO (Paid), MoI - Moment of Inspiration (Paid) and Autodesk Alias Design (Paid).
Rhino can create, edit, analyze, document, render, animate, and translate NURBS* curves, surfaces, and solids, point clouds, and polygon meshes. There are no limits on complexity, degree, or size beyond those of your hardware.