Cisco IOS XR

IOS XR is a release train of Cisco Systems' widely deployed Internetwork Operating System (IOS), used on their high-end Network Convergence System (NCS) and carrier-grade routers such as the ASR 9000 series and Carrier Routing System series of routers.

According to Cisco's product literature, IOS XR shares very little infrastructure with the other IOS trains, and is instead built upon a "preemptive, memory protected, multitasking, microkernel-based operating system".

[1] The microkernel was formerly provided by QNX;[2] versions 6.0 up to 7.5.2 use the Wind River Linux distribution.

[3] From version 7.6.1 and onwards, the kernel has been switched to OpenEmbedded.

More examples can be found in the Cisco document Converting Cisco IOS Configurations to Cisco IOS XR Configurations.