A free alternative to classroom clickers

Now any teacher can have a Classroom Response System (or Classroom Performance System) for free with this alternative to clickers.

Let me start by saying
Happy Teachers' Appreciation Week! 
For this week, I decided to go with an Android app. It's gaining a lot of traction among teachers and counselors. It's "paper clickers" or Plickers.

It's a simple app that allows to check responses from students by simply turning their piece of paper with the 2D Code.
According to Plickers:
"Plickers lets you poll your class for free, without the need for student devices. Just give each student a card (a 'paper clicker'), and use your Android smartphone or tablet to scan them to do instant checks-for-understanding, exit tickets, and impromptu polls. Best of all, your data is automatically saved, student-by-student, at plickers.com."