The Cyrus project was originally started at Carnegie Mellon University but it has since attracted a very dedicated and diverse group of core contributors. Carnegie Mellon University remains active in development of Cyrus and also provides the infrastructure on which cyrusimap.org runs today, but CMU is now just one of many core contributors to Project Cyrus.
These are the core organizations who are providing dedicated resources to the Cyrus Project.
FastMail is a leading e-mail hosting provider that runs on Cyrus software.
Kolab Systems AG is the developer of the Kolab Groupware system, of which Cyrus IMAP is a core component.
Isode Ltd is a renowned developer of open-standard e-mail, instant messaging, and directory software. Its internet servers use Cyrus SASL for authentication.
Carnegie Mellon University
Carnegie Mellon University is a global research university with more than 11,000 students, 86,500 alumni, and 4,000 faculty and staff.
There are also individuals who have dedicated their time to Project Cyrus in various ways including answering questions on the mailing lists and IRC channel, writing code, testing new releases, etc. This isn't going to be a complete list by any stretch. If I left anyone off this list it's because I have a bad memory and not because your contribution wasn't appreciated.