This is mainly a bugfix release but also includes new features to support recently-introduced and forthcoming Duet3D products. Please see the change list at https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x#reprapfirmware-361.
The files here are for users running Duet in standalone mode. Users running with attached Single Board Computer should upgrade from the Duet3D package server as usual.