Pyxis 2 is an OS running on the .Net Micro Framework (NETMF). It can theoretically run on any NETMF platform, but it is currently configured only for GHI Electronics (Tinyclr.com) products.
To learn more, read the NETMF team blog or visit the official site. The code is available as open source at pyxis2.codeplex.com. Here is a video to whet your appetite:
Pyxis 2 Beta Released!