We’ve heard of computer aided design — but here is a system that aids the physical rendering of a design with a pen by using magnets to lock vectors into straight lines and curves into perfect circles,
via DigInfo.tv:

This table helps you to draw precise freehand circles and lines. It is under development by a group in the Yasuaki Kakehi Lab at Keio University.

By using a computer to control the XY position of a magnet under the surface of the table, it implements, on paper, drawing methods utilized in computer graphics.

“I’ll place an ordinary ballpoint pen on the table. Now, I can semi-automatically draw a precise circle, or a straight line, or an illustration prepared in advance. In other words, while I draw with the pen, this system lets me switch to accurate rendering like in computer graphics, such as drawing a precise circle, by assisting me with the pen.”

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