Looking for Real-Time Unixes

[News system owner ID]

I'm currently evaluating Unix solutions for use in a current project.
My first leaning is toward a "real-time" Unix and I've looked at Lynx
Real-Time Systems' offering which seems to be quite good, but I'd like
to hear other recommendations. Please include a company contact if you
have it.

Also, I'm interested in hearing about the limitations of standard
Berkeley Unix in a real-time environment. What are the specific
problems and is there a way around them?

Thanks for any responses!

Regards, Mike Slocombe