Disclosure: I work for Google.
It appears to have been archived in Japanese, but: https://web.archive.org/web/20120103092225/http://to/
Some large orgs maintain internal shorteners, like http://go links at Google.
If you set your dns search path to example.com then http://go would resolve to go.example.com which could be your link shortner.
Do you happen to know how Google, or any other places, do this? I assume a custom DNS resolver being forced on clients through a network could do this, or maybe hosts files for each machine.
This often bites people when they wonder why they blow up their DNS servers with traffic from services that contact addresses like "foo.default". With a search path of "search default.svc.cluster.local svc.cluster.local cluster.local" in resolv.conf, the app is actually looking up foo.default, foo.default.default.svc.cluster.local, foo.default.cluster.local, and foo.default.svc.cluster.local, etc. every single time. Hard-code "foo.default.svc.cluster.local." in the app config, and you eliminate requests for the names that can't possibly exist, and save the load (and latency) of handling them.
It seems that the service now redirects to a site called Freenom where you can still get .tk names, but they appear to be priced based on the length and whether or not the domain contains known words or phrases (though some free ones are apparently still available if you don't mind having a gibberish name)
IIRC, anything that isn’t the TLD is a subdomain. It’s just that we typically think of a subdomain as starting at the third-level. So, for this site, news is the subdomain of ycombinator.com, but also, ycombinator is a subdomain of com.
I consider that virtuous, and smart. Short domains must cost more than long domains. They're more valuable. Words must cost more than gibberish. But there were domains available, right? Didn't have to bang out twenty minutes finding something you liked that wasn't taken?
People who discuss the internet publicly generally assume that a TLD implies renting out large numbers of domains to the public. IMO, that is only one potential use.