Many moons ago I got my first home computer: an Apple ][c. Included with my shiny new Apple were a set of disks with demos, guides, and utilities, many of which were written in AppleSoft BASIC. The interactive capabilities of BASIC were pretty rudimentary, and on these disks there were BASIC programs that seemed to be doing more.
So I took a look at the source code for these programs and lo and behold, Apple had built themselves library of custom BASIC commands that were tied to the & character (so instead of using INPUT they would use &INPUT and so on). This custom library was a simple binary file, and if you loaded that file into memory you could use the nifty new commands in your own programs. This added a lot of polish to what were otherwise simple BASIC programs. Other programmers learned about this, and soon many libraries were available with custom BASIC commands.
I hope Apple will release this library for public use. It would be awesome. Even if they don't, like the old BASIC library this new library shows what's possible.