Model Design :
SketchUp (free) (paid)
SketchUp is a 3D modelling program for a broad range of applications such as architectural, civil, mechanical, film as well as video game design — and available in free as well as ‘professional’ versions. Download for OSX
OpenSCAD is a software for creating solid 3D CAD models. It is free software and available for Linux/UNIX, Windows and Mac OS X. Unlike most free software for creating 3D models (such as Blender) it does not focus on the artistic aspects of 3D modelling but instead on the CAD aspects.
Slic3r is the tool you need to convert a digital 3D model into printing instructions for your 3D printer. It cuts the model into horizontal slices (layers), generates toolpaths to fill them and calculates the amount of material to be extruded.
Skeinforge is a tool chain composed of Python scripts that converts your 3D model into G-Code instructions for RepRap.
Printer Control :
This is the software that will drive your MakerBot Replicator, Thing-O-Matic, CupCake CNC, RepRap machine, or generic CNC machine. You can give it a GCode or STL file to process, and it takes it from there. It’s cross platform, easily installed, and is based on the familiar Arduino / Processing environments. ReplicatorG is used by thousands of MakerBot Operators, and has printed tens of thousands of 3D objects and counting.
RepetierHost can crteate G code for printer based on the models. The software can slice the models and determine the print path. The printer instrcutions can be saved to SD card for standlaone printing (not connected to PC). Download for OSX