BusyBox
BusyBox is a multiuse-utility, designed for embedded Linux-systems.
For example, BusyBox is used in Tiny Core Linux.
BusyBox can provide most of the functionality of the many programs typical found in /bin, /sbin, /usr/bin, /usr/sbin, /usr/local/bin, all in a single binary, thus saving space on small systems.
As a shell, BusyBox provides ash.
BusyBox can be configured to include as little or as much "applets" as desired.