From the Cheetah3D website:
"Cheetah3D is a lean, fast and elegant 3D modelling, renderering and animation tool for Mac OS X with an easy learning curve. It offers many tools from powerful polygon editing over advanced subdivision surface modelling to HDRI and radiosity renderings. Support for many common 3D file formats rounds up its feature set."
The newer versions of Cheetah3D work great with Unity. To import models from Cheetah3D, simply place them somewhere in your project's Assets folder and they should be automatically imported.