Not comparable to Cyanogenmod, but Microsoft at one point officially supported the WP jailbreak tool and its developers, Chevron. The logic was, of course, to get more apps developed for WP. Unfortunately, after a while, they found out nobody jailbroke their phones to develop apps, so both parties agreed to stop supporting it, and later updates revoked the jailbreaks.

Not to mention Firefox OS and Ubuntu Touch (both made possible by re-using low-level parts of the Android stack).