Real Time Java

A reference implementation of RTJ was released recently by timesys.com .

Its a GPL implementation, that runs on their GPL version of Linux 
called Timesys Linux.

While going through the document, found that you can schedule events 
down to a nanosecond. This means that the RT specification does not in 
any way change the java specification (remember the nanosecond option 
in many commands that were unused till now).

It also comes with a TCK (Technology Compatibility Kit) which means 
that if you modify the VM and wish to distribute your change, it must 
pass the TCK tests.

The VM and TCK come in 3MB, and are free.

Timesys also sells a GUI development kit for some 2800 USD.

Remember its a reference implementation and thus not very optimized.