Coincidentally on the front page, https://news.ycombinator.com/item?id=45989650

ARM also used to have opcodes for Java: https://en.wikipedia.org/wiki/Jazelle

Haha, I was the one who submitted it after going down a rabbit hole from this :)

Sun JavaStation: https://en.wikipedia.org/wiki/JavaStation

I was aware of these, it's kinda what I meant by "None of these were really Java Machines". They were just shitty sparc machines that had Java OS in flash. It didn't have some kind of Java co-processor and still relied on a JVM. Java OS was pretty neat but I wouldn't really consider it a "Java OS" since it was basically just a microkernel that bootstrapped a JVM from what I've read. An actual Java machine IMO would have to at least have some kind of Java co-processor and not rely on a software based JVM

Sun also tried, and failed, to bring to market, a microprocessor architecture for running Java on metal - https://en.wikipedia.org/wiki/MAJC

In theory you could say that simcards were / (are?) Tiny java on a chip machines.

There were a lot of efforts to accelerate the JVM in hardware, the one i remember is the ARM "Jazelle" extension https://en.wikipedia.org/wiki/Jazelle

Azul Systems was making Java machines a while ago.

There were attempts to create a "Java Machine". Apart from JOP that is mentioned in another comment there were other systems that had a whole OS written in Java, a stub interrupt handler written in assembler would call into Java for any event.