Comment by joshuaissac

OpenJDK includes HotSpot and the class libraries. OpenJDK licences do not cost money, even if you use the one from Oracle past a certain patch point. Builds of OpenJDK from other vendors like Red Hat and Microsoft are based on the OpenJDK source code from Oracle.

Oracle JDK is the non-free version that shares the same code base as OpenJDK. Oracle provides a restricted licence for this build, under which it is free to use in certain cases, up until specific patches. Later patches (usually a few years after the initial release date) require a licence fee. This does not apply to Oracle OpenJDK, which is released under the GPL.

If you want to avoid HotSpot altogether, the other options include Graal (used with OpenJDK class libraries), IBM OpenJ9 and IKVM.NET.