There is no tech secret sauce to reddit. Reddit is a good experience because of unpaid moderators who care a lot. There is a reason quality of content on reddit is higher than similar websites like quora.
The various alternative reddits that have popped up in the past prove the tech stack isn't complex. Their lack of user adoption shows that the secret sauce is the userbase, not the tech.
>Reddit is a good experience because of unpaid moderators who care a lot.
Arguably they care too much, and a bit of humbling will be good for Reddit. If the powermods had their way Aimee Challenor would still be working for the site.