RNS is an extension given to files used by the software of the Swedish development group Propellerhead Software called Reason. RNS are files containing music projects made in the program. They do not contain any audio data by themselves, but they do store all the information needed to properly reproduce the project as well as information about the location of the actual audio files used in the project.

Propellerhead Reason is an advanced digital tool that is a virtual music studio.