Bent Ruler

This Bent Ruler by Tomoya Yoshida is made of a flexible plastic that requires finger pressure on top to keep it flat on the paper.

At first glance, a bent ruler is terribly unintuitive; however, it actually solves several problems that plague conventional rulers:

1. In drawing straight lines, pressure needs to be applied to the ruler to prevent slipping.  The bent design actually forces the user to apply this pressure, reducing the chance of sideways motion.

2. The ruler springs back up after usage, making it easier to pick up from the page.

3. The ruler's edge does not lie in contact with the paper after using, preventing smudging. 

Of course, several criticisms can be launched against it as well.  First, it's more difficult to use it for measuring real objects (screen sizes or table lengths, for instance).  Storage may also become a problem.  While it can be compressed flat for storage, the tension might make it snap easier.  

Despite the shortcomings, though, it's still an excellent design.

Source: Via Yankodesign