Debian is a UNIX-like operating system composed entirely of free software. Most of the software included is licensed under the GNU General Public License and is packaged, developed, and maintained by a team of participants in the Debian Project. It is famous for being a guideline, for adhering to the spirit of Unix and free software, and for the many choices it gives users. Many companies choose Debian because of security and stability considerations. In terms of stability, Debian distributes security patches quickly; in terms of stability, in addition to providing support for up to 5 years, it also provides a smooth upgrade plan to the next version.