I've always wanted a simple interface to help my students practice the unit circle. I've found Quizlet sites that help with this, as well as the occasional Khan Academy exercise that approaches what I want. The big issue I find with most of these is that the interface and the questions ask much more than what I'm looking for. I want a simple flashcard-like situation with no bells and whistles that gets my students the repetition and opportunity to think through the functions with feedback.
The live site can be accessed here: http://codepen.io/emwdx/full/bgEJYK/
This is essentially a digital version of a set of flash cards, but they never stop. The angles rotate around the unit circle and the trigonometric function used is randomized. Since I am holding my PreCalculus students responsible for the reciprocal functions, but my IB students don't need them, I added the ability to flip those on and off.