If I had to chose the one climbing technique that greatly expanded my ability on rope, it was the signal foot lock. It replaces the foot loop Prusik. Obviously there's a litany of hardware with foot loops where it acts as a substitute. It's a technique for the minimalistic climber. Moreover it provides all rope users a way to load a rope by using one foot.
The single foot lock is a foot inserted into a loop. There's a very specific orientation of the loop. Just as your feet are mirror images of each other, the same is true for the loops that work on each foot. The right foot requires a "p" loop. The left foot takes a "q".
When you lift your foot and point your toes up, the locking mechanism releases, and the rope magically flows over your foot, allowing your leg to progress up rope. Point your toes down again to repeat the locking step. The illustration below is the right foot with the "p" loop.