I belong to several groups on google and someone shared this link for quick and easy formative assessments. It has some really nice ways to use formative assessments. In addition most of these suggestions could easily be done on mobile devices.
One suggestion is using concept maps and on mobile devices any mind mapping app would work well. Exit cards could be done by having students create QR codes with a QR code maker, write the answer on a white board and showing you. The one minute essay could be done in an e-mail, a google doc, a word doc and sent to you. I printed off the information to pin up on my bulletin board.
Over the weekend I hope to work with Mathtoons new create your own quizzes app for several classes. I'll let you know how that goes.