MathChat is an excellent resource for teachers and students. At our school some students do their best learning at home or late at night, when there is not a teacher present. On MathChat however there are students waiting to answer other questions as well as teachers.
I can answer student questions at 9 o'clock at night or when I have a substitute teacher and I am out of the building I can help students that are struggling. One new thing I have started doing in class is offering students extra credit offering their help to other students. It provides them insights on steps and explaining their thinking.
MathChat continues to update their product and is free on the App Store. You can find their website here: http://math.chat/. Wonderful resources all teachers should be using in their classroom inside and out.