AskBot is an open-source StackOverflow clone that has a hosted option. (Easier than hosting it yourself, since correctly installing can be tricky.) AnswerHub (

AskBot is an open-source StackOverflow clone that has a hosted option. (Easier than hosting it yourself, since correctly installing can be tricky.) AnswerHub (formerly Qato) is a managed clone of Quora for orgs. They caused quite an uproar because they originally hewed much too closely to Quora's design. [edit: I see that AnswerHub is now more like StackOverflow.]