Cemetech user here, although I pretty much stopped going there, as I was more into Casio calculator stuff and nowadays there's not much development activity for these. I must say I envy the large community support for the TI calcs, especially the older z80 ones, which are really really well understood and have been reverse-engineered in every way possible.
I kind of got into reverse-engineering the Casio Prizm, but eventually gave up because the SuperH is a much more complex architecture than the Z80; also, the firmware is so much bigger and not very well understood, it's hard for a beginner to dive in. That more or less explains why there's no such thing as a KnightOS for Casio calculators.
I'm part of that group that learned more about computers and programming with his calculator, than math. Which was actually a very good outcome, since in this undergrad computer engineering course, calculators are mostly forbidden, but the knowledge I got from them is quite useful :)
Hey! Made an account just to reply. I used to lurk on both Omnimaga and Cemetech pretty frequently several years ago. I remember when the original OS signing keys were first factored as well as the bootloader debacle later on with newer calculators. I still check in occasionally to see what cool new hacks are going on nowadays.
Fellow Omnimaga user here... I don't post on my account much though; I mainly just used it to tell some people I got Android running on my NSpire CX. From what I've noticed, however, it's a very friendly community.