Gforth is a fast and portable implementation of the ANS Forth language. It works nicely with the Emacs editor, offers some nice features such as input completion and history and a powerful locals facility, and it even has (the beginnings of) a manual. Gforth employs traditional implementation techniques: its inner innerpreter is indirect or direct threaded. Gforth runs under Unix, Win95, OS/2, and DOS and should not be hard to port to other systems supported by GCC.
ICI is a general purpose interpretive programming language that has dynamic typing and flexible data types with the flow control constructs and operators of C. It is designed for use in many environments, including embedded systems, as an adjunct to other programs, as a text-based interface to compiled libraries, and as a cross-platform scripting language with good string-handling capabilities.
KernelDriver automates your Windows 2000/NT, Windows Me/98/95 and Linux device driver development by providing you with powerful tools for hardware debugging, driver code generation, and driver debugging. KernelDriver supports PCI / USB / ISA and EISA drivers. KernelDriver for Windows and Linux includes the powerful Driver Wizard. Using the Driver Wizard you can graphically debug your hardware by "peeking" and "poking" at it without writing a single line of code. After your hardware is diagnosed, use the Driver Wizard to generate a complete kernel mode device driver which will drive your hardware.
Mercat is a light-weight, cross platform programming language. It is garbage collected and self hosting and produces portable byte-compiled binaries that can be executed on any platform with the appropriate interpreter. Interpreters are available for Linux, DOS (32-bit) and DOS (16-bit) and the interpreter source should be easily compilable for other platforms.
RPilot is an interpreter for the IEEE-standard programming language PILOT written in portable C. PILOT is a language that was designed in the 1960's to support computer-aided instruction and is very simple to learn. RPilot comes with an introduction to the language and several examples.
SmallBASIC is a free interpreter for BASIC, a simple computer language, targeting simplicity, mathematics, and graphics. Also, it has a powerfull string library, supports external C modules (shared libs), uses dynamic arrays (by default) and has no data types. Versions exists for Linux (or other Unix), PalmOS, DOS, Win32, VTOS (Helio), and Franklins (eBookman). It uses a lot of drivers, including svgalib, ncurses, and framebuffer.