Classcraft is described as 'Watch students become better learners as they level up, work in teams, and earn privileges to help them succeed' and is an website. There are four alternatives to Classcraft, not only websites but also apps for a variety of platforms, including iPad, Windows, Android and Android Tablet. The best alternative is Foldit, which is free. Other great sites and apps similar to Classcraft are ClassDojo, @MyClassGame and LABSTER.
Foldit is an experimental video game about protein folding, developed as a collaboration between the University of Washington's departments of Computer Science and Engineering and Biochemistry (many of the same people who created Rosetta@home).