BusyBox provides several stripped-down Unix tools in a single executable. It runs in a variety of POSIX environments such as Linux, Android, FreeBSD and others, such as proprietary kernels, although many of the tools it provides are designed to work with interfaces provided by the Linux kernel. It was specifically created for embedded operating systems with very limited resources. It has been self-dubbed "The Swiss Army Knife of Embedded Linux". It is released as free software under the terms of the GNU General Public License.