I know StackOverflow is only public, but I'm looking for free open source software like StackOverflow.

The posts I found are really old ones or paid and charge too much for me like AnserHub and AnserBase I'm looking for something like http://www.mkyong.com/featured/top-5-open-source-qa-systems/ (These projects are old and not maintained).

I tried PhpBB but it is far different from StackOverflow.

Do you have a good Q&A or forum solution?

The features I would appreciate:

  1. Subscribe to tags by getting emails.
  2. Admin console.
  3. Add Images/ attach files.
  4. Open source.
  5. Large development community.
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    Welcome to Software Recommendations! We will need much more information to give good recommendations here – asking for "a tool like X" is never giving enough details, even if linked. You should always list your requirements explicitly. Please see How to ask for an alternative to some software and the questions linked to it for details. What features do you need? What would you rather not like to have? – Izzy Jan 4 '16 at 18:44
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    The solutions there is out dated, or not on premise – Mark T Jan 4 '16 at 22:12
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    @MarkT To make your case, what I would do is make a note at the top of your question, stating that you are aware of that question and maybe give a brief explanation as to why you asked a new one. – aman207 Jan 4 '16 at 23:24
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    And maybe in here there are also candidates: meta.stackexchange.com/questions/2267/stack-exchange-clones – user416 Jan 5 '16 at 9:04