I was on the #Pump.io
site yesterday and found a wiki page about servers. Not the usual Pump servers, but servers that provide services that most federated socnets generate from each instance.
For example, RagTag\.io was to provide hashtagging for the network. There were statistics hubs, a firehose, a find-your-friends service, and more. The repositories are still there, mostly without being touched for 6-8 years, but the primary service point (such as ofirehose\.com and ragtag\.io are almost universally gone, replaced by domain squatters and the like).