The Java Virtual Machine (JVM) was certainly not the first virtual machine (ADA, at least, was there before...), but it is a pretty popular one.
Several - if not many - languages can now be compiled into JVM byte code, and as such, they run for free wherever a JVM exists. Among them, Scala, Groovy, Clojure,... the list is long.
In short, all they need to provide is a compiler, the runtime is provided by the JVM implementation.
More to come about that..., stay tuned!