Java VMs that do not require an operating system?

What is it you need?

Perhaps Sanos can give you a small chunk of code between the hardware and the JVM which you can use?

http://www.jbox.dk/sanos/

Unlike SANOS, the JNode operating system is a full operating system with many supported devices, file systems, a network stack, a GUI stack, a command shell and 50 or so commands, and much more. JNode currently runs on x86 (32 bit) with one processor enabled, but x86-64 and multi-processor versions are in development. (JNode is 99.99% Java. Porting to a new architecture would entail rewriting the 0.01% of code that is in assembler, creating / modifying hardware specific drivers ... and writing a native code compiler for the new architecture.)

We currently have ~7 active developers, but we are always looking for new people to join the team, especially people who understand Java AND code generation, garbage collectors, drivers and so on.

(And for what it is worth, we use a recent version of the OpenJDK class libraries: 1.6u24 at the last count.)

There's also Project Guest VM, which is a JVM hosted on Xen hypervisor. While the home page seems to be rather light on details, there's a Google Tech Talk about this project as well.

There is the Sun project Squawk which a VM that runs on hardware instead of an underlying OS. Useful for embedded devices like the Sun SPOT where Squawk is the OS.

Squawk is licenced under GPLv2.