Microsoft qbasic

The basic 3D programs use qbasic, a BASIC interpreter and full-screen editor first bundled with version 5.0 of MS-DOS. qbasic is a large subset of the Microsoft dialect of BASIC supported by the QuickBASIC 4.5 compiler, a DOS-based development system. In most cases, qbasic source code can be used in Microsoft Visual Basic and most other BASICs without much modification.

If you're running Windows, try typing qbasic at a DOS prompt. With any luck, it's already installed in a directory on your default PATH. Otherwise, you may have to find it on your Windows CD (in \other\oldmsdos\ on the 95 CD, or \tools\oldmsdos on the 98 CD, for example) or scrounge up a different BASIC (several free ones are available for download). To run a qbasic program, start qbasic, load the program, and press F5. Press F1 for context-sensitive online help. Press F2 to navigate among subroutines, which are otherwise hidden from view.

The main attraction of qbasic, and the reason the programs on these pages are written in the qbasic dialect, is that it's free, and you may already have it.