The Femto OS is a very concise portable preemptive operating system for embedded devices with minimal ram and flash, up to say 16K flash, 1K ram. The main target is the AVR architecture, such as the ATtiny861/461/261 series.
Open source project that offer summary and download services on this page is a project that carry out their development work on other open source development sites. Their work is linked to this page via a feature called OFI, and their work is not carried out here on OSDN site.