[jwmittag]

OMR is the Open Managed Runtime. Basically, IBM took their Java implementation (the J9 JDK), or more precisely, J9's Java Virtual Machine implementation, separated all the language-specific and VM-specific parts from the language-agnostic and VM-agnostic parts, broke it up into independently re-usable modules (memory manager, JIT compiler, garbage collector, profiler, debugger) and released it as Open Source Software under the umbrella of the Eclipse Foundation.

Ruby+OMR is the proof-of-concept project that aims to show that OMR is indeed language-agnostic and VM-agnostic and can be used as drop-in parts not only for newly-designed VMs but also easily integrated into existing VMs. The Java 8 version of IBM's J9 JDK is already built on top of OMR, but you could consider that cheating, since that's the very VM OMR came out of; Ruby+OMR shows that you can also do that with languages other than Java and VMs that have a different design than J9.

I believe there is also a Python+OMR project which does similar things with the CPython VM, but that project is not (yet) public, AFAIK.