H-ITT SoftClick
(Virtual clicker, requires a good web connection)
***YOU WILL STILL NEED TO REGISTER SOFTCLICK ON THE WEB REGISTRATION SITE, if your teacher instructs you to do so.

THIS IS NOT AN APP - students purchase a subscription that can be utilized from any web browser (via a Smart phone, tablet, laptop, etc.) to respond to questions posed by instructors in class.
http://www.h-itt.com/support/SoftClick.htm

The iCue is a handheld RF (Radio Frequency) transceiver that is used by students or audience members to respond to questions posed by the instructor. They have 13 buttons for up to 10 response choices A-J or 0-9, forward and reverse keys for indexing through test questions, and a multi-function button for changing RF channels, or special status functions. When a response key is pressed, the light on the remote turns red, and when the response is successfully received by the base unit the light on the remote will turn green giving user confirmation the response was received.

The iCue Pro is a handheld RF (Radio Frequency) transmitter that is used by students or audience members to respond to questions posed by the instructor. The remotes have 20 buttons and provide responses (student answers) ranging from simple multiple choice to multi-digit, alpha-numeric answers. A HI-RES LCD provides user visible confirmation for text answers, plus status fields that make for ease of use. The iCue Pro is two-way; both the LCD screen and a green light on the remote provides confirmation the response is received.