I have been interested in computers with stack architectures for a long time. I wrote a bit about one of the latest versions at ECN a while back: Testing The GA144 Eval Board . For those of you not familiar with the subject I thought it might be a good idea to present some resource material.
The place to start for an overview is Phil Koopman's book Stack Computers  which is available as a free e-book. You can read it online or down load an html version for local reading. You can also buy the book or download a free pdf version from Lulu. Links at the above link.
Harris at one time made chips in the RTX series called the RTX2000 . I still have the RTX bags from a trade show. Plastic bags. Which just goes to show you how dedicated I am. Intersil took over making a rad hard version for space - the RTX2010RH . You can still get the data sheets  but they are no longer selling the chip.
Phil Koopman also wrote up a computer science type paper comparing RISC, CISC, and STACK architectures . He says stack architectures have advantages. I agree with him.
As you can see from this scan of Patent #4,980,821 , the patent on machines of RTX version of the architecture have run out. I wonder if any chip maker who wants to differentiate themselves in the market will pick up on the idea and run with it. A machine with a lot of RAM, FLASH and a number of different types of I/O might go over big. Especially when you consider that using FORTH cuts development time in half compared to C. An then there are PLCs wich run a version of FORTH called Structured Text . The PLC market uses a lot of chips. When you make your hardware conform to your high level language there are speed gains to be made. Or price reductions from using less silicon.
M. Simon's e-mail can be found on the sidebar at Space-Time Productions .