The pictures tell the story here. Developed in Spain by Kiko Luna, the OKLine can be used in a number of configurations. The classic elevated aimline is shown in the video below. What's nice about the product is they have marked it at 1 and 2 meter intervals so you can tell how far away you are from the hole in addition to being able to practice longer putts (up to 10 meters). The videos are in Spanish.
This video shows a typical chipping configuration where the instructor has created a 1 meter square box as a landing target for short game visualization. If you have a second OKLine you can attach it to the flag to see how far your balls are from the hole. For example you could extend it out to 1 meter, 2 meters, 4 meters and stick tees in the ground to make circles.
Lastly in the full swing configuration you can use the OKLine like an adjustable alignment stick. Create a V shape as shown, or 2 parallel lines. It is even possible to make a plane indicator by attaching the string to a belt loop on your right or left hip.
Besides the videos make sure to look at the additional photos (beneath the main photo above) because it shows the product more clearly than the videos. OKLine is very reasonably priced, has a nice golf design and can be used to work on every aspect of your game. Special pricing if you purchase two.