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.
Windowed OS is going to be a kind of "virtual OS" running as an native app, with own virtual hdd, console and GUI. It will be possible to develop apps for it and it will be possible to run it without installation, as an portable executable file.