They’re all Oracle’s version. OpenJdk is Oracle’s implementation of the JLS. They’re just not using Oracle’s build of OpenJdk.

Almost all.

Embedded folks with real time offerings like PTC, Aicas, microEJ,.... have their own implementations, with real time support, bare metal deployments.

Folks like IBM and Azul nowadays take parts of OpenJDK, mostly standard library, and add their own runtimes instead.