Prulu is described as 'stores, organizes and presents your class Q&A in a simple, intuitive interface equipped with a smart search engine - and it's free. Check it out' and is an website in the Education & Reference category. There are three alternatives to Prulu, not only websites but also apps for a variety of platforms, including Windows, Mac, Android and iPad. The best alternative is Hypersay. It's not free, so if you're looking for a free alternative, you could try Piazza or Glisser.
Hypersay is a platform for interactive presentations that massively increase engagement. Keep your audience engaged with polls, questions, private notes and live slide sharing. Store, enrich & deliver presentations from your cloud.