Basic Decompiler: A DOS Basic decompiler. Author also offer a text recovery service to anyone who has lost their Basic source code.
BCX: QBasic-to-C converter to run and compile QBasic programs in C.
FreeBASIC: A free 32-bit MS-QuickBASIC's syntax-compatible compiler for Windows, that adds new features such as pointers, unsigned data types, inline-assembly. [Open source, LGPL]
QB2C: QuickBasic to C converter. Installation and programming support, sample and working program downloads, latest releases and sales information.