McNeel's Rhino 3D has recently expanded into OSX territory. Here's an intro webinar that gives a sense of it in use:



The vast majority of CAD jewelers are using Rhino because it offers a tremendous set of tools to create/describe surfaces. The intricate ways that jewelry is designed should give a clue as to Rhino's suitability as a modeling program. In this thread, I used a pre-release version of Rhino OSX to model a brain just to see how far it can be pushed for organic objects:

http://discourse.mcneel.com/t/anybod...th-rhino/10981

An added bonus is that Rhino ingests and outputs to numerous other formats. All the nURBS objects I've created in Rhino have always exported cleanly to STL (for 3D printing) without issues. (Watertight, no naked edges, etc)

If the products you work with are more stodgy and mechanical, the alternative is to pay Autodesk their ongoing subscription fee and use a product like Fusion360 for OSX.