OpenWrt

highly extensible ​GNU/​Linux ​distribution for embedded devices ​(typically wireless routers)

OpenWrt is an operating system for network devices, such as wired and wireless routers, firewalls, and switches. OpenWrt can be used to run many routers from different manufacturers. It replaces the original factory firmware. OpenWrt can add enterprise features, such as VPN support, to inexpensive home routers.