Since the HP42s, then has not been any significant development in Scientific calculators, at least in the RPN flavor. When HP released the HP30b calculator, it provided also a Software Development Kit with it. The machine used a well known third party chipset, and had a Pogo connector for upgrading software. Some aficionados saw the opportunity of creating the best RPN calculator ever.
It has all the mathematical functions you can imagine, and then some; it can have a 4 or 8 level stack; and it has many constants you can use in your equations. And, of course, it is programmable.
We install the latest version of the WP34s firmware on a brand new HP30b calculator;and we supply an adhesive overlay with it (we have found that customers prefer to collate the key labels themselves. We have reduced the price from 94€ to 75€ for our Black Friday.