This is the software publisher’s description.

As far back as 1999, a group of visionary LEGO product developers and engineers started thinking about letting people design their own LEGO products. They imagined people of all ages, anywhere in the world, being able create any design they could dream up – using an intuitive, free tool for digital design.

The first milestone was achieved in July 2003, when version 1.0 of LEGO Digital Designer was released. In February 2004, an online 3D Gallery went live, allowing designers to share their ideas via the Internet. By 2005, thousands of LEGO Factory enthusiasts were designing, sharing and ordering their own custom models – and the one-millionth copy of LEGO Digital Designer was downloaded on 25 September that year.

LEGO Digital Designer is quite simply the best virtual building system out there – with its “Click-Stick” method of 3D modelling winning praise from children, parents, teachers and design enthusiasts everywhere. And, as the virtual design platform behind a growing number of LEGO products, LEGO Digital Designer is here to stay. A host of improvements and new features are already in development, including an improved user interface, new connectivity, more life-like building, Technic compatibility and improved train building and animation. So stay tuned – with LEGO Digital Designer, the future is yours.

Note that this is the Windows download and is Windows XP only. An Intel Mac OS X version is available from the LEGO Digital Designer download page.