OpenSCAD is a free software for creating solid 3D CAD objects. It is open source software that is available for Linux/UNIX, MS Windows and Mac OS X – and also a version that runs online in browser. After quick testing it looks like OpenSCAD is a really wonderful tool for 3D modeling. While it doesn’t have the traditional graphical interface of AutoCAD – it’s basically a programming language for 3D models – OpenSCAD is able to create very complex parts with only a few lines of code. OpenSCAD allows for two types of modeling – constructive solid geometry, or taking 3D primitives and stretching, scaling, and intersecting them to create a 3D shape, or extrusion from a 2D outline. It should be sitable for making desings for 3D printing as quite a few RepRap parts were designed in OpenSCAD and Makerbot 3D printer maker has OpenSCAD tutorials for this in mind.
If you want to start experimenting with OpenSCAD parts in your browser. There are two alternatives for this. OpenSCAD.net offers one online version of OpenSCAD that runs nicely at least on Chrome browser (failed to work properly in Firefox for me). It is a nice playground to test OpenSCAD.
Does coding your 3D objects, while quite easy, still look too complicated to get started. There are also some alternatives that are even easier to get started. BlocksCAD is Browser-Based 3D Modeling that Teaches You CAD. MIT has come up with a new block-based educational tool called BlocksCAD. BlocksCAD is essentially Scratch combined with OpenSCAD and allows the user to use blocks (similar to Scratch) to build a 3D model. With this tool it’s possible to avoid model code syntax issues but still develop 3D models. You just make model by moving blocks, and get a 3D model and OpenSCAD code as result. You can use the tool online at blockscad.einsteinsworkshop.com
For ideas on other 3D modeling tools, check out also Scratch Your Itch for 3D Modeling with BeetleBlocks, Learn 3D Modeling in Your Browser and Development Tools of the Prop-Making World articles.