1. External Documentation
OpenWRT uses, both officially and unofficially, many third party components with only minimal changes. Often, additional documentation is provided by the creators of these components.
1.1. BusyBox
OpenWRT uses BusyBox to implement most of the normal unix commands. Instead of having a collection of binaries, they are all condensed into one. Executables like ls and grep are merely symbolic links to the busybox binary.