FunkOS is an RTOS for 8-32 bit MCUs including AVR, MSP430, and Cortex M3. Both C and C++ kernels avaiable. Key features include preemption, periodic events, device drivers, and mutex/semaphores. Includes a variety of graphics and filesystem middleware. Please also check out FunkOS's big brother, Mark3OS. Mark3OS is slightly larger, but is more scalable, much more feature-rich, and supports a wider variety of devices.
Funk51 is a portable Intel 8051 emulator designed to run on embedded MCU's including AVR, MSP430, and Cortex M-3. 8051 programs can be included with the emulator as C arrays, or run from external SPI flash or SD media with the appropriate drivers.