Embedded Linux OS for Nios II processor

FreeRTOS & ChibiOS/RT are other open source operating systems that have NIOS II ports. I have used ChibiOS/RT on NIOS myself and was happy with its very small footprint (<1MB).

Each open source RTOS will have their own pros & cons; just depends on which one fits into your end application needs. For example, many linux/rtos distros require the use of an MMU along with NIOS. This could be more difficult to port or you may not have (or need) resources so you may want to go with simpler OSs that can run without MMUs.

AFAIK altera does not maintain its own linux distro (unless you want to classify HAL as an OS). The NIOS SBT does come with demo examples for MicroC OS II and many altera application notes have implementations using the same; its not open source though.

I have not come accross any linux os that was built specifically keeping NIOS II in mind. Most of them are generic and in theory can be ported to