[nwatson]

The Gates company make the Gates Carbon Belt to replace bike chains with a carbon fiber belt (encased in some polymer). My Priority Bicycle 600x has this belt drive, along with matching sprockets and a Pinion C1.12 "transmission", where all gearing/shifting takes place.

To check proper tension, Gates supplies an app [0] that also has you pluck the belt to measure the frequency. For my bike the appropriate tension is at 60Hz. Tension is adjusted by moving the rear axle backward or forward.

[0] https://play.google.com/store/apps/details?id=com.gates.carb...

EDIT: the advantages are ... no fragile derailleur; no chain lube; long belt lifespan; low maintenance