OpenWrt is a Linux distribution for embedded hardware. Instead of trying to cram every possible feature into one firmware, OpenWrt provides only a minimal firmware with a a fully writable rootfs and support for add-on packages. For users this means the ability to custom tune features and removing unwanted packages to make room for other packages. For developers this means being able to focus on packages without having to test and release an entire firmware.
OpenWrt is free software, provided AS-IS under the terms of the GNU General Public License.