Top 5 open source Q&A platforms for 2021

I’ve assembled a list of the top open source Q&A platforms that are currently available. The list contains only projects which are in active development and have a working demo site. There are a few similar blog posts out there but they’re quite outdated. Most of the projects listed below are inspired by Stack Overflow which is in fact the most popular community for questions and answers related to programming. Please, bear in mind that the list is not ordered in any way.

Discourse -

Website: https://www.discourse.org
Language: Ruby, Rails
Database: PostgreSQL
License: GPL 2
Commercial support: Yes
Demo: https://try.discourse.org

Scoold -

Website: https://scoold.com
Language: Java, Spring
Database: Any (database agnostic)
License: Apache 2.0
Commercial support: Yes
Demo: https://demo.scoold.com

Askbot -

Website: https://askbot.com
Language: Python, Django
Database: MySQL, PostgreSQL
License: GPL 3
Commercial support: Yes
Demo: https://askbot.org/en/questions

Vanilla -

Website: https://open.vanillaforums.com
Language: PHP
Database: MySQL
License: GPL 2
Commercial support: Yes
Demo: https://open.vanillaforums.com

Question2Answer -

Website: https://www.question2answer.org
Language: PHP
Database: MySQL
License: GPL 2
Commercial support: Yes
Demo: https://www.question2answer.org/qa/