Busybox is quite well known project, but frankly from the way you write about it, it does not look like you know how it works so apologies if I'm explaining something that you already know.
Busybox is a reimplementation of the standard linux utils (ls, find, dir, etc..) for resource limited machines. To quote from the man page:
> BusyBox is a multi-call binary that combines many common Unix
> utilities into a single executable.
How it works is that it symlinks the binary to each of the commands it implements and then it executes the corresponding functionality based on the value of argv[0].