RMG v0.6.6 is released. Rosalie's Mupen GUI is a free and open-source mupen64plus GUI written in C++. It offers a simple-to-use user interface.

RMG changelog:
Fix mupen64plus-core URL in the about dialog
Fix GLideN64 not showing native path seperator in the configuration dialog (see gonetz/GLideN64#2860)
Add 'SDL controller mode' option to the options dialog of RMG-Input
Add 'None' option to configuration file of mupen64plus-input-gca (thank you @GhostlyDark)
Update GLideN64, mupen64plus-core and SDL_GameControllerDB

Download: RMG v0.6.6
Source:Here