busybox is a replacement for a multitude of Unix utilities. Commonly used on embedded systems, it combines commands like
tar into a single, tiny executable. The busybox versions of these utilities are very minimalist; the options they accept are sparse compared to their GNU equivalents. While busybox can replace most of the utilities you usually find in fileutils, shellutils, findutils, textutils, and others, it's modular design allows each command to be included or excluded at build time.
A symbolic link named after each utility that busybox replaces can be pointed back to the busybox executable, and busybox is smart enough to know what to do when invoked from one of these links.
busybox was originally written by Bruce Perens for Debian rescue and install floppy disks. It is currently maintained and supported by Lineo, an embedded Linux vendor.