Syllable Desktop is a complete operating system that is easy to use, powerful, lightweight and extraordinarily fast and responsive. It has its own kernel, filesystem, GUI and applications. Syllable Server is a matching small and efficient Linux server.
ButterflyOS is a very simple operation system for the Atmel AVR Butterfly board. It's based on the AvrX multitasking scheduler, created by Larry Barello. A byte-code program for ButterflyOS, can be sent and managed through the serial interface.