Planarity is a puzzle based on a concept by Mary Radcliffe at Western Michigan University. The player starts out with a tangled series of connected dots, and has to untangle the web until none of the connecting lines cross.
Not as easy as it sounds; tho' not as difficult as untangling your daughter's skipping rope (or the chain on your husband's medallion ;o)
This version of the game supports 5 modes of play on iPhone, iPod Touch & iPad; plus GameCenter integration, so you can beat your friends' best times. Oh...and the puzzles are auto generated...so no in-app-purchases are necessary!