This must be broken in sub-tasks and as many plugins. You can edit this list as needed since it’s now an editable wiki 
Existing plugins : .
- Discourse Feature Voting – vote ont the topic popularity
- Discourse-qa - Discourse Question Answer Plugin – vote on answers and sort them according to popularity
- Discourse Solved (Accepted answer plugin) – green checkmark for author’s recommended answer
- Babble Chat – chat
- Convert all existing topics in category to wikis
Non existing:
- How to get answer’s comments? (stackoverflow-like & tiny)
- How to have all post (answers) as wiki by default?
- Stackoverflow gamification vs Ethics of reputation: Proposal and Critique
Note1 : please turn your question into a wiki so we can collaboratively assess this issue’s progress.
Note2 : As of Fall 2018, Stackoverflow opens a team service https://stackoverflow.com/pricing