OSQA!

Stack Exchange is a fast-growing network of 84 [and counting] question and answer sites on diverse topics from software programming to cooking to photography and gaming. We are an expert knowledge exchange: a place where physics researchers can ask each other about quantum entanglement, computer programmers can ask about JavaScript date formats, and photographers can share knowledge about taking great pictures in the snow.

A Q&A site helps an online community to share knowledge. No matter what your area of interest, people with questions can get super answers fast. Question2Answer is a popular Q&A solution.

Askbot is a Q&A system, like StackOverflow, Yahoo Answers and some others. Askbot is based on code of CNPROG, originally created by Mike Chen and Sailing Cai and some code written for OSQA.

Yahoo! Answers is a way to find and share information. You can ask questions on any topic, get answers from real people, and share your insights and experience.

Bitfortip offers a unique use case thanks to Bitcoin.

Coordino allows you to create a question and answer system for you and your users to enjoy.

Shapado is a questions and answers site for your enterprise or community, your “knowledge base on the cloud”. It makes sure questions never get asked twice by making the information flow.

Scoold is inspired by StackOverflow and implements most of its features. You can ask and answer questions, upvote and downvote posts, earn badges and reputation. Each edit creates an new revision, making it easy to follow the history of edits. Scoold is optimized for the cloud. You can simply click the 'Deploy to Heroku' button and get up-and-running in minutes. You can deploy it to your favorite PaaS, too.

Glisser makes presentations interactive – it takes regular PowerPoint or Keynote slide decks and pushes them out live to audience mobile devices, slide-by-slide, as they are presented. It then enables members of the audience to interact with the presenter or each other, and collects valuable feedback. Attendees can also electronically mark-up the slides with notes, and keep them for future reference.

AnswerCart provide a community platform to the businesses which can be integrated with websites or mobile apps. Using community, users can engage in Q&A, blogging and socialization or in short we help organizations to build their own forum like Quora or StackOverflow.

Askalot is a next generation CQA (Community Question and Answer) system.

Answerbase looks to offer enterprise grade social Q&A to websites of every size, in a web platform that is easy to setup and manage.The platform is built and managed by Lumin Creative, who has been powering Q&A communities for some of the world’s most popular websites for years. Through Answerbase, Lumin Creative brings this powerful social Q&A platform to sites at every level. Our team is comprised of professionals and engineers with years of experience providing Q&A and social media solutions. Companies such as Edmunds.com and Angie’s List can attest to the fact that with Answerbase you can count on an outstanding product with reliable service and support.Answerbase offers a free trial as you get a feel for the service and has pricing tiers that will satisfy any level of client. Whether you are a startup website or blog or one of the most well trafficked sites in the world….we can serve you. With pricing starting at $15 per month, take a look at our available tiers today to see which one fits your needs. »

BitAsker is a paid question and answer plateform using Bitcoin ... a user can win money by answering a question.

Niko gives us all a way to surface important questions, ideas, and concerns in a way that decision-makers and stakeholders can engage constructively before small problems become big ones. Unlike bulky, “sad-making” HR software, Niko is the single-purpose, simple, and intuitive solution to make sure everyone feels heard.