People don't realize that Reddit *used* to be open source. https://github.com/reddit-archive/reddit
GitHub - reddit-archive/reddit: historical code from reddit.com

historical code from reddit.com. Contribute to reddit-archive/reddit development by creating an account on GitHub.

GitHub

Another thing people find surprising:

Self-hosted Reddit servers used to be commonplace.

@atomicpoet
The only major extant server based on the old Reddit source code, to my knowledge, is called "Saidit" (how original...) and is basically a den for all the subreddits that got banned from Reddit proper, so take a quick guess on what kind of content does it have