Back in the early 2000s, the IBM JVM was freely available and frequently used as a drop-in replacement for the Sun JVM, since it was often faster and less memory-hungry.
IBM also had an open-source Java compiler written in C++, Jikes [1], that was considerably faster than Sun's javac. However, it was eventually abandoned. Jikes is coincidentally also the name of IBM's open-source research JVM [2], which is still under development.
Azuul is apparently popular in areas requiring low latency, such as financial trading.
As an aside, there are many niches that most people haven't heard about. You might be surprised about all the kinds of software that are hiding under rocks — invisible to most people because they're not working in that industry. Things like MUMPS, K/kdb, Fortran, Delphi — lots of obscure stuff that has left the mainstream (or never entered it in the first place) but is still in use.
Jikes RVM was known as Jalapeño first, then they changed the name to Jikes RVM due to a name clash (Jikes Java compiler already existing at the time). I'm not sure it is still active though, a lot of researchers left IBM a few years ago (2012) and Java ceased to be the hot topic anyways.
IBM also had an open-source Java compiler written in C++, Jikes [1], that was considerably faster than Sun's javac. However, it was eventually abandoned. Jikes is coincidentally also the name of IBM's open-source research JVM [2], which is still under development.
Azuul is apparently popular in areas requiring low latency, such as financial trading.
As an aside, there are many niches that most people haven't heard about. You might be surprised about all the kinds of software that are hiding under rocks — invisible to most people because they're not working in that industry. Things like MUMPS, K/kdb, Fortran, Delphi — lots of obscure stuff that has left the mainstream (or never entered it in the first place) but is still in use.
[1] https://en.wikipedia.org/wiki/Jikes
[2] https://github.com/JikesRVM/JikesRVM