uClinux is an operating system that is derived from the Linux kernel. It is intended for microcontrollers without Memory Management Units (MMU's). It is available on many processor architectures, including the Blackfin processor. The official uClinux site is at http://www.uclinux.org/
The source and documentation found here is specific to the Blackfin processor. If you have any questions about uClinux for the Blackfin processor please ask them here.