CP/M is really open source now
-In 2001 a limited licence for using CP/M was given to Tim Olstead (The Unofficial CP/M Web site) by Bryan Sparks who was (and still is) CEO of Lineo (successor of Caldera).
This licence has been clarified by Brian Sparks, CP/M is now clearly under an open source licence.
Source code of CP/M (different versions) is available, also their respective manuals.
You will find more informations about CP/M on John Elliott's web page.