Mir is a pretty notable example. In 2013, around the same time development on Wayland sessions was picking up for the other desktops, Canonical decided to try doing their own incompatible thing and designed their own display server system to replace X for the then-upcoming version of their Unity desktop.

Ubuntu switched from Unity 7 to Gnome 3 before Unity 8 and Mir were ready, leaving both projects abandoned by Canonical and handed off to the community. Long after it had already lost what little relevance it had, Mir eventually was converted into a Wayland compositor.