James Garfield, when not proving the Pythagorean theorem, could write simultaneously in Latin with one hand and in ancient Greek with the other.

Thea Alba (left), “the woman with 10 brains,” toured Europe in 1920 displaying her ability to write in French, German, and English at the same time and to draw a landscape in colored chalk using both hands at once.

You can produce mirror writing by holding a pencil in each hand, writing normally with your dominant hand, and willing the other hand to match it.