Thanks, I stand corrected about the CPU

So Sun Network Computers were JavaOS on SPARC, Oracle were NCOS (Acorn RiscOS derivative) on ARM – and I think IBM's had a similar tech stack to Oracle's...

were there any others?

Correcting myself:

IBM Network Station used PPC

And although its OS was called “NCOS”, it was completely different from Oracle’s NCOS. It was apparently a closed source derivative of NetBSD