Hydra (operating system)

HYDRA is an early (now discontinued) capability-based, object-oriented microkernel designed to support a wide range of possible operating systems to run on top of it. HYDRA was created as part of the C.mmp project at Carnegie-Mellon University in 1971.
The name is based on the ancient Greek mythological creature the hydra. 
HYDRA was designed to be modular and secure, and intended to be flexible enough for easy experimentation.
The system was implemented in the programming language BLISS.