A: Too many. So Fortune examined six—testing them out and speaking to their CEOs—to bring you a roundup of how each site works and which one might best deliver the answers Internet surfers seek.

By Daniel Roberts, reporter

Q: Have you noticed the sudden explosion of sites purporting to offer Q&A? Have you taken note of the wild press given to some of them (ahem, Quora), wondered if the attention is deserved, and wished you could know the differences between them?

A: We have, and we've investigated each site. No two are exactly the same. A lot depends on how you want to access (online, mobile, or email), and what type of question you have (factual, or more advice-based). The Q&A space will continue to change as new startups bite into the market.

Q: Is there any easy, obvious way to compare them across the board?

A: Naturally, our chats with the minds behind these sites is the best source, but for good measure we also came up with one knowledge-based question that requires some experience and cannot be answered by an easy, searchable fact. We posed it to each site's community in order to test its strength: What is the best way to prepare for a journalism job interview at a legal publication?

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