Since the source code for this site isn't available for purchase or external use, I'm looking for software that can run a Q&A environment similar to Stack Exchange. Are there any such pieces of software available?
Stack Overflow for Teams, a hosted solution, is available for use. In the past there was an enterprise version of Stack Overflow, but this is now deprecated.
But if that does not meet your needs, there are several third-party tools that try to clone at least some of the functionality here.
Most active that look like the best bets
Not open source
AllAnswered: Django. Include Q&A in its knowledge management system. Not Free.
Haydle: SaaS, free 30 day trial. Haydle is focused on being a private, internal Q&A system.
SabaiDiscuss: commercial WordPress Plugin
Tribe: SaaS, freemium plan. Tribe allows you to build your own social app (including internal or external Q&A sites).
Unity Answers: Allowed topics are the Unity editor and C# (the site is free and in English)
Ones that look sort of finished
shapado: Ruby, mongomapper and MongoDB. AGPLv3. Website unreachable, Last commit in 2012.
openoverflow: Ruby, PostgreSQL, Haml. MIT license. No example site, and I can't find anyone using this one. Not a lot of recent activity; last code commit, May 2009.
phpancake: PHP, Zend framework, MySQL. Live site. MIT license. Last activity Jan 2013. Renders very poorly in some browsers; the live site states "I am aware of this site not working properly. I am working on it!".
Rootbuzz: (site down) Django, hosting, actively developed, non-free
Programlama: Python, flask (In Turkish)
cahoots: PHP, MySQL. GPL, MIT license. Officially inactive; demo site offline; last update Aug 2010.
Solace: Inactive; last commit in 2010.
Kliqqi: PHP, MySQL. Different look, hosting available. Not active, CC-BY 3.0 license
stacked: ASP.NET, Ra-Ajax, ActiveRecord ORM. GPLv3.
Arrayshift Drupal plugin GPLv2, last commit in 2016.
Kunjika: Rust, Actix, Sevlte and Postgres. GNU GPLv3 or later.
Others that seem to be work in progress
Asking: Perl, Mojolicious. Perl License (Artistic). Little documentation at this point. GitHub repository README.md in Portuguese.
kerjakelompok: No example site. Unknown license. Little info.
SmartR: No example site. MIT License. Little info.
Stack Underflow: C#. No example site. License is "do whatever you want with it" (I haven't defined a formal license yet). Written as a learning project.
T002_rails-overflow: Ruby on Rails. No example site. Unknown license. Little info. Apache license.
CNPROG: Python/Django.Project officially closed. Was used as base by OSQA & Askbot.
Veaos: MERN (MongoDB, Express, React and Node.js)
Sorted by language
- Q&A (Is a WordPress Plugin)
- Vanilla Forums
- OSQA (merged to AnswerHub)
Rootbuzz(site down, last tweet dates back to 2013) Programlama(site down)
- openoverflow (last commit in 2009)
- T002_rails-overflow (last commit in 2009)
SmartRCreator announced it is deprecated.
- QARoR (barely any progress)
- Discourse (active, primarily a discussion forum)
MEAN/MERN (MongoDB, Express, Angular/React, and Node.js)
Did I miss any? Disagree? Please add a comment or update this answer.
I am currently following Codidact with some interest.
Codidact is a work in progress and fairly new, but describes itself as:
A community-controlled, open-source Q&A platform.
Splunk Answers appears to be running some sort of Stack Overflow clone.
The logo in the bottom-right corner says "Powered by Khoros" but I have been unable to locate which product exactly they are using. The marketing materials I have looked at so far seem inconclusive, but I'm guessing it's Khoros Atlas.
As you can tell from a few minutes on the site, the software by itself does not work very well if the user base is not taught how to curate. In the absence of a culture to engage with new answers and upvote good content, and downvote incorrect, off-topic, or unhelpful posts, it's just another digital landfill.