What is the sndr format?

.sndr MS-DOS early ’90s .SND(RT) files

SND is a file extension for a sound file used with a variety of platforms. SND stands for SouND. SND files may contain audio data specific to a Macintosh sound resource (from Mac OS Classic), an AKAI MPC audio sample, a generic Amiga sound, or other audio file. SND files can often be opened by Apple’s Quicktime Player