BitVisor is a tiny hypervisor initially designed for mediating I/O access from a single guest OS. Its implementation is mature enough to run Windows and Linux, and can be used as a generic platform for various research and development projects.
ChibiOS/RT is a free and efficient RTOS designed for deeply embedded applications. It offers a comprehensive set of kernel primitives and supports many architectures: ARM7, Cortex-M0, Cortex-M3, Cortex-M4, PowerPC e200z, STM8, AVR, MSP430, ColdFire, H8S, x86.
scmRTOS is tiny Real-Time Preemptive Operating System intended for use with Single-Chip Microcontrollers. scmRTOS is capable to run on small uCs with as little amount of RAM as 512 bytes. The RTOS is written on C++ and supports various platforms.
An open source COBOL compiler for the PC x86-32 platform.
Generates GNU assembler and requires GCC to produce a binary.
Supports Linux, BSD and MinGW 32 bit platforms.
A hardware supported hypervisor originally built for malware analysis. Features: Linux VM introspection, minimal detectability, small (~150KB), simple, and well documented. Can be used for other purposes. Support for Intel-VT & Windows coming soon.
Tiny C compiler, programmed in C with compiler/linker/assembler included. VERY fast and mainly usable as a library. WIN32 port of the http://tinycc.org version. Compiles code to memory currently, perhaps disk soon. Go to the homepage for more info.