Stack Exchange isn’t a direct question and answer site itself, but rather an aggregate of all the free, community-driven question and answer sites in its network. For example, if you had a question about photography you would visit photo.stackexchange.com. The main Stack Exchange page displays the currently “hot” (as in popular) questions so you can browse threads created by others, or you can browse all the Stack Exchange sites to find a place to ask a question of your own.
Quora is a great question and answer community that has a goal of building answer pages for virtually every question you could think to ask. Though still young, the tech crowd is quickly embracing Quora and enjoying the process of providing good answers to good questions. If a particular topic interests you, or even another member of Quora, you can follow it/them to keep yourself up to date.
Google really needs no introduction. For most of us, it’s our go-to search tool that helps us find answers to the majority of our questions. It’s simple, it’s fast, and it’s effective.
Wolfram Alpha isn’t a site for any question, but the answers you’ll get to the questions you can ask are answers you won’t find anywhere else. For example, you can use Wolfram Alpha to calculate activity-specific calorie burn, analyse illness symptoms and generic drug options, and make sense of your confusing family relationships. It’s a great way to ask a question and get an answer with a wealth of meaningful data.
With Aardvark, you put a question out into the ether and Aardvark finds someone to answer it in under a minute. This is not a pay service, but simply a network of people who are looking to help others. When you sign up for an account, you choose topics you know about so when people ask questions in those categories you’ll be notified and can provide an answer. When you ask a question, others are notified so they can help you out. Aardvark is simply an effective tool for people to help each other get meaningful answers to simple questions.