L4 is a family of second-generation microkernels based on the original designs and implementations by German computer scientist Jochen Liedtke. Originally implemented as highly tuned Intel i386-specific assembly language code, the API has seen extensive development in a number of directions, both in achieving a higher grade of platform independence and also in improving security, isolation, and robustness.
The L4 µ-Kernel Family Homepage: http://os.inf.tu-dresden.de/L4/
The L4/x86 was the original design developed by Jochen Liedtke at GMD, IBM Watson Research Center, and Universität Karlsruhe.
Assembler Source Code: http://www.acm.uiuc.edu/white_papers/incoming/GMD/L4/
Reference Manuals: http://os.inf.tu-dresden.de/L4/l4doc.html