New in my "code compost" bin: in 2015 i threw together a simple silly demo of a webring backed by @matrix rooms, Matrix rooms can store non-linearized "state events" attached to a room & replicated to every server, effectively a distributed key-value store
This idea is conceptually similar to how Matrix plans to decentralize and democratize moderation policies and reputation lists https://matrix.org/blog/2020/10/19/combating-abuse-in-matrix-without-backdoors
MSC2313 proposes a semantic for encoding policies as state events which can be replicated/user-service'd https://github.com/matrix-org/matrix-doc/blob/msc2313/proposals/2313-moderation-policy-rooms.md
When I was doing 5-10 interviews a week at my last job, we spent a lot of time thinking about interview questions. Once i jokingly proposed that junior engineers should design a webring service and senior engineers should design a webring without a central store. I never used it in an interview, but took the inspiration and presented this implementation.