A Linux distribution is an operating system made as a collection of software based around the Linux kernel and often around a package management system. A typical Linux distribution comprises a Linux kernel, GNU tools and libraries, additional software, documentation, a window system, window manager, and a desktop environment. Most of the included software is free software/open-source software which is distributed by its maintainers both as compiled binaries and in source code form, allowing users to modify and compile the original source code if they wish. Other software included with some distributions may be proprietary and may not be available in source code form. Linux distributions are almost universally Unix-like as described; the most notable exception is Android, which does not include a command-line interface and programs made for typical Linux distributions. There are currently over six hundred Linux distributions; over three hundred of those are in active development, constantly being revised and improved. One can distinguish between commercially backed distributions, such as Fedora (Red Hat), opens USE (SUSE), Ubuntu (Canonical Ltd.) and Mandriva Linux (Mandriva)[1], and entirely community-driven distributions, such as Debian, Slack ware, Gentoo[1] and Arch Linux.