Phoenix
An operating system, built in BCPL on top of IBM MVT and later MVS by Cambridge University Computing Service from 1973 to 1995, which ran on the university central mainframe. All parts of the system were named after birds, including Eagle (the job scheduler, also the nearest pub), Pigeon (the mailer), GCAL (the text processor) and Wren (the command language), leading to Wren Libraries (a local pun).
Phoenix was much used by chemists in daytime and by the rest of the university in the evenings, and was only abandoned in favour of Unix in 1995; it is one reason Cambridge made little contribution to Unix until then.