Rolleiflexes and Rolleicords had an accessory 35mm kit with an insert and gearing spools etc, to enable the cameras to shoot 35mm film. Earlier (pre 1950) Rolleis could also be converted using a full 35mm back, I have one of these which I found very cheaply at a deceased estate. It works perfectly on all Rolleis, even my 2.8E2.
The one flaw is the Rollei TLRs then have to be used sideways for horizontals so they are best for portraits and close ups of pots of pretty flowers etc. Landscape shooters would be most annoyed.
An old friend has converted (with much effort and even a little blood) a 616 folding camera into a nifty 35mm shooter. Like others, he enjoys the visible sprocket holes as part of his images. Everything he has shot with this home made gadget has been mostly out of focus except for the infinity shots, and otherwise quite terrible, but we haven't the heart to tell him, he is so proud of those images and his efforts.
Like Sirius Glass (#11), I use mine one or two times a year for the fun of it. As a play thing, fine. For serious work, no thanks.
Posted entirely Without Prejudice, just sayin'...