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.]

If I worked for a big company, I'd love this (or, a Quora for a loose social network like HN people, YC companies, attendees of a series of security conferences, a university department, etc.). Makes a lot less sense for a 3 person startup (at that scale, email and/or wiki makes more sense).

I think Opzi was also potentially this at one point in the past, but just like everyone else doing "enterprise Q&A", pivoted away. I think there's no way to build something which makes money, is simple, is usable and worth using, and complies with stupid enterprise policies on Q&A.

Ditto, I'd like it if they would offer it out as a whitelabel solution.

It's much better away of dealing with somethings than an FAQ or endless forums.

It's possible, but run the numbers. Companies that would pay for that * monthly price = ?

Very hard to justify a Twitter-like valuation with that.

Yes its true, they can't be twitter but they have a fine product which can be monetized without taking away from their shoot for the stars plans.

I always believe in having a profit, so when you fail in shooting-for-the-stars you fail into profitability, stability, and the dolldroms of merely having six figures in your salary instead of eight in your stock portfolio.