The reusable launch vehicle (RLV) concept has now been partially demonstrated for big conventional rockets, but sustainable reusabilty is still awaited
The Swala RLV has sustainable reusability. This means
it is able to price its payloads well below any rivals.   At the Swala lift-off speed of 400km/h, its ramjets can have the same thrust as solid fuel rocket motors.
To find out why, read this   A PDF presentation on Swala can be downloaded here