Junos OS (more formally Juniper Network Operating System) is the FreeBSD-based operating system used in Juniper Networks hardware routers.It is an operating system that is used in Juniper's routing, switching and security devices. Juniper offers a Software Development Kit (SDK) to partners and customers to allow additional customization. The biggest competitor of Junos is Cisco Systems' IOS. Junos OS was formerly branded as Juniper Junos, and is commonly referred to as simply Junos, though this is a general brand name of Juniper Networks, including other product lines such as Junos Fusion.