I have 2 Canon RFs - a "P" and a "7". They take LTM lenses of which there are many made by Canon, Nikon, Leica, Cosina (Voigtlander) and many others. I have a Nikon LTM lens that is particularly good. There are 3 common RF body systems: Leica M -- the newest system 1954 I think; Nikon RF system and the Leica Thread Mount (AKA Leica Screw Mount) which includes Leica "Barnack" cameras (the original Leica), Canon, and several other manufacturers. All have there adherents. Cameraquest's website has some info about this.