This release sent me down a rabbit hole (it started with the sidenote on physics), which made me wonder what software https://discuss.python.org is running on. I couldn't find a link to GitHub or elsewhere or any project page which could enable me to host such a discussion board on a server. Does it have a name?

I'm fairly sure it's Discourse[1]. They switched to it quite recently.

[1] https://www.discourse.org

From the HTML source code: