Our Unison and DSPnano RTOSs are 100% Linux compatable in code and have very similar but non gpl licensing. It also has a tiny tiny footprint with a minimal size of less than 1.6K bytes and complete I/O solutions (tcp, serial, multimedia file system, ...)
http://rowebots.com/products/unison
http://rowebots.com/products/dspnano
http://rowebots.com/Embedded_Processor_support/renesas_m16c_development
http://rowebots.com/Embedded_Processor_support/renesas_H8SX
http://rowebots.com/Embedded_Processor_support/renesas_R32
Let us know if you're interested in early work.
Kim
PS ... We are very interested in an Sh2 port as well. If you are interested, please contact us.