Updated. Apple iPad owners have the $10 AirDisplay app to use their tablet as a second monitor for their Mac, but Android owners aren’t left out in the cold. Mobile app developer Shape offers a similar program for $5 that turns allows Android devices to be a second monitor for Macs or Windows PCs. The software is called iDisplay and it recently gained some updates in version 2.1. I’ve been using it on a 10-inch Android tablet with my iMac and it works as advertised although it’s not quite as responsive as AirDisplay for iOS.