It was the 28 then the 48 I did the most programming on: A trip computer for recording time, distance, fuel consumption, and miscellaneous notes. And HHTS--hand-held timing and scoring. Take it to the race track, enter names and numbers of 6 competitors, push the corresponding key when they cross start/finish. Display either lap times or gaps.
My Dad turned me on to the 48G, inadvertently. He was actually a fan of the Commodore calculators (of C-64 fame, yes, they made calculators). And the 15C.
Notably he was fond of push button programming, and the simply the fact the functions were on the keys.
He got a 48G when his Commodore finally died.
What boggled my mind when dabbling with the 48 was that it had Kermit built in.
Kermit is a file transfer protocol (like X-, Y-, and Z-Modem from back in the day). Which meant the G had a serial port. Of all things.
"A what!?"
Where I was working they were toying with some handhelds for data collection in the field (well, the green houses). They had some awful thing already and were looking at some devices from Symbol.
But since these things had Kermit, as well as a just everything else (things like menus, forms, and the function keys etc. etc.), I managed to convince them that we use these instead. The fact that they were $99 each instead of $999 each helped seal the deal. They also lasted for-ever on the 3-4 AAA batteries that they used. Weeks. They were tough too. One got run over by a truck and came out ok. We got these nylon fluorescent orange cases for them.
They'd take them out, record their data, return them, and then a guy would plug them in to a PC and we'd upload the data in to the computer. It was pretty slick.
Programming the 48 is truly just a joy. It's super powerful with RPL (Reverse Polish Lisp), it's easily factored, easy to test, and you can do it in bed. Most of the coding for this thing was done in my spare time with pillows.
People did absurd things with the 48, they had that all figured out. I didn't need to go to those levels. I was able to use the high level routines for everything. It was pretty amazing for a 4-bit CPU.