Piazza is a Q&A and discussion platform designed to simulate real class discussion. It aims to get high quality answers to difficult questions, fast.
A wiki is a website where users can easily add, edit and delete content without specialist software or technical knowledge. Users can create new wiki pages and link them to others, and they can edit existing pages, including those created by other learners.
For several years now wikis and blogs have both been widely used in Higher Education. Both are platforms for easily publishing material to the web and both provide a platform for feedback. Both are ideal for learner-centred activities with learners taking part in collaborative tasks aiding knowledge construction. And both can be used to deliver rich content for learners to absorb.