I want to see if this has been done, or attempted. I don't even know what to call it, so I'm using the analogy of 'Analogue' gearing (so no gears)

Bassically, instead of gearing up in a 'digital' fashion where you have a set torque at each gear, you have a perfectly smooth graduation from torque.

I have thought of this once before and the only concept that comes to mind is an expandable sprocket/cassette. Has anyone ever been so far to go do look more like? I know it's a dream, but I also know it's not strictly impossible to achieve so if it's even been prototyped and failed, I'd really like to see the mechanics others have proposed to solve this.

PIC Not related, strictly speaking that would fall under 'digital' (correct my terms if you have a better phrasing)