Network Operating Systems
A network operating system (NOS) is a specialized operating system for a network device such as a router, switch or firewall.
e.g. OpenWrt, pfSense, VyOS, Cisco NX-OS
components have been optimized to be small enough to fit into the limited storage and memory available in home routers.
Cisco NX-OS
For the Nexus-series Ethernet switches, Closed source. NX-OS is built on a Linux kernel, and it natively supports the Python language for creating scripts on Cisco Nexus switches. (Cisco IOS is not on Linux) Nexus is primarily for data centers.
The NX-OSv 9000 is a virtual platform that is designed to simulate the control plane aspects of a network element running Cisco Nexus 9000 software. The NX-OSv 9000 shares the same software image running on Cisco Nexus 9000 hardware platform although no specific hardware emulation is implemented.
VyOS
VyOS: a virtual router, running as virtual machine. a Linux-based network operating system that provides software-based network routing, firewall, and VPN functionality' and is a Firewall in the security & privacy category
Vyatta is a software-based virtual router, virtual firewall and VPN products for Internet Protocol networks
The system is a specialized Debian-based Linux distribution with networking applications such as Quagga, OpenVPN, and many others.
Vyatta is also delivered as a virtual machine file and can provide (vRouter, vFirewall, VPN) functionality for Xen, VMware, KVM, Rackspace, SoftLayer, and Amazon EC2 virtual and cloud computing environments.
The free community Vyatta Core software (VC) was an open source network operating system providing advanced IPv4 and IPv6 routing, stateful firewalling, secure communication through both an IPSec based VPN as well as through the SSL based OpenVPN.
In October 2013, an independent group started a fork of Vyatta Core under the name VyOS.
VyOS runs on a wide range of hardware from small office routers to large servers, as well as virtual machines and multiple cloud providers.
pfSense
pfSense is a firewall/router computer software distribution based on FreeBSD. The open source pfSense Community Edition (CE) and pfSense Plus is installed on a physical computer or a virtual machine to make a dedicated firewall/router for a network.