Hum, any punbb dev's program for Palm OS pre V5.x. I believe since Palm OS v1.0 and up to palm OS 4.x you could "hook" into system functions.
Here's an example:
I want to display a little "X appmnts." message in the title of every palm OS app I run.
I could hook into the function that's called to display ~palm os windows~ (can't really call them windows... but you can't not...). Once my custom function is hooked, instead of calling the APIs original version of the function, only my version is called. In my function, I call the original APIs version of the function, and then, I call a function to rename the window, so as to add the "X appmnts." to then end of it's title.
Then I want to use joe's function hook that does the same thing, only his displays the time at the end of the title bar. I hook joe's function to that same call. the API now called joe's function. joe's function think my function is the original version of the function, and calls my function. My function calls the original version of the function, then renames the title bar and returns. joe's function then renames (the renamed) title bar and returns.
Doing it this way allows for a static number of "hookables" to do an unlimited number of things. One could quite easily replace a 100 line function, with a light weight, 20 line version; or simply add a few extra commands in before or after that function, and edit the output of the function to place their results in the middle. Then again this was a full fledged API, on a tiny device mind you, so a tiny API.
I have no clue what 1.3 extentions are like though...