Four years ago, Erik McMillan went shopping for a timer to keep him on pace during his LSATs and made a discovery -- there weren't any. So he and wife Christina decided to make one. The Silent Timer, which tells students how much time they're spending on each question during the SAT, LSAT, and other exams, is now available in more than 400 college bookstores.

Ages: Both 25
Location: Austin, Tex.
Revenue: $250,000
Employees: 3