Artisan is a plugin for SketchUp, an organic toolset that works pretty much like the terraforming tool in Second Life. It’s a commercial product, price is US$39.00.
Quoting from the web site:
Artisan is a set of powerful organic modeling tools. It builds upon the subdivision tools in Dale’s previous plugin, Subdivide and Smooth, and adds new tools to SketchUp that provide unprecedented control over complex high-poly forms.
While subdivision modeling is the core of the plugin, the sculpting and soft transformation tools allow you to take your models even further. Artisan gives you the power to model things that were previously not possible in SketchUp.