Also see nullroute hosts.
Nullroute doesn't run anything serious, it is just a place for experiments. This means that servers come and go, the services are often misconfigured, the only account is "
grawity", and there really isn't anything worth offering.
That said, I've learned a lot by simply tinkering around with various network services. And it's much easier to study a working implementation than hundreds of pages of RFCs, so that's what I'm doing here. (Much like other people pretend they run an army of elves…)
I sometimes grab copies of various old websites or FTP sites (frequently just weeks before they go down). A few of those are accessible as mirrors.
Three's a small collection of interesting Usenet and mailing-list posts which is accessible through anonymous IMAP, at
imap://email@example.com/Public and subdirectories.
Other things that may or may not be running at any particular moment: