Earlier quoted context omitted.
discourse is open source, you can put it on a raspberry pi
Then you have to pay for a domain name (which granted is cheap), setup something to handle your IP changes, install and maintain the pi itself and hope there aren't any vulnerabilities that can be exploited to gain a foothold in your home network, which means segragating it behind a VLAN which your ISP router probably doesn't support so you need to buy a router then of course you need to buy the pi it self and an SD…
TBH it’s kind of weird to hear someone bemoan running a raspberry pi on hn. You could also use Digital Ocean for $5 a month, I think they have a one click Discourse install. I guess running your own stuff is old fashioned.