Crochet for Gadget is an application helps to create a crochet for any size of rectangular gadgets (phones, electronics, DIY projects, etc.). Measure the size of the gadget and type in a form, the app generate a crochet pattern fit for the gadget. It has a built in pattern player. If there is a change in pattern the app will say it aloud the number and type of next crochets. The pattern can be walked through manually with a Bluetooth button or automatically with a timer. The app support statistics: full length of yarn, time need, and project cost etc.
Tutorial: http://www.instructables.com/id/Crochet-for-Gadget