Some virtual Lego builders include the Lego Digital Designer, BlockCad, LDraw and Bricksmith. The Lego Digital Designer is the official Lego computer aided design program for Windows and Mac. Conversely, BlockCad is unofficial freeware, but although it has fewer design options, it works well on less modern computers.
LDraw is a more advanced type of freeware, and its independent community project is recognized by Lego and is partially compatible with the Lego Digital Designer. The project provides an extensive collection of freeware tools that cater to advanced modeling, design and imaging. LDraw runs on Windows 98 and above, Mac and Linux. Bricksmith is a similar program to LDraw; however, it only is compatible with Macs.