Web-based discussion tool (not a full-fledged learning management system, but you can link to Piazza from your LMS, including Blackboard, Moodle, and Coursera) that allows student to ask questions and interact with instructors and other students in a public space. A wiki style format enables collaboration in a single space and features LaTeX editor, highlighted syntax and code blocking. Questions and posts needing immediate action are highlighted and instructors endorse answers to keep the class on track. Anonymous posting encourages every student to participate. Subjects include computer science, biology, chemistry, economics, psychology, engineering, mathematics, and physics. Once in a subject area, you can view what professors from where are teaching or answering questions on what.
This is a great tool for students looking to get extra or more in-depth help beyond the classroom.
Companies can use Piazza for recruiting college students, and it is this function for which users pay.