I have a CASIO Graph 90+E, which is effectively an fx-CG50, which is effectively a tiny little computer with a SuperH CPU. And, of course, I make software for it.
It's not even that hard to get somewhere: installing custom software is a matter of dragging its binary, and maybe a couple of extra files! Even better is that people can make their own with publicly available community SDKs and tooling. I like using fxSDK with gint, as it has support for a lot of libraries, makes your code run mostly separately from all the OS syscall mess, and I can even claim to have a "CASIO" MIDI keyboard !
Outside of calculators, I still think that owning a little device you can have control over to do generally stupid projects is something worth doing, even just for the hell of it.