Request for suggestions: algebraic equations in Free42

[Thomas Okken]

I am thinking about creating a paid version of Free42, with some of the enhancements I have been asked to do over the years, but didn't do because I felt they would take too much of my time to implement, like a big screen, big stack, units, and algebraic equations.

I am looking for inspiration about how to approach the algebraic equations in particular. I'm not looking to create another RPL machine, there are plenty of those already, and that really would be far too big a project for me to consider... but I know there are other, non-RPL, HP calculators with algebraic equations that people like, and maybe one of those would be a good starting point.

What machine would you recommend for me to look at? The 27S, 19BII, 35S, something else? Anything that I could run as an emulator to play with, or would be able to buy without spending an arm and a leg, and without having to embark on a restoration project, would obviously be preferred.

(I'm not making any promises yet as to whether this will ever see the light of day. Think of it as a feasibility study for now.)