Interesting domains!

.youtube top-level domain is pretty interesting, it was made so certain youtube channels could host content on it, it was implemented in 2014 but it's still unused. Source 1.

.google and .goog, like the one above these are also owned by google and can only be used by them. This is used by google to provide their own corner of the internet for example and Right now some of google's sites are still on .goog, like Source 1. Source 2.

.godaddy is a top-level domain said to be used by godaddy to protect their branding, i looked in the network requests of their site and it seems to be unused. Source 1.

Here are all top-level domains for anyone interested (Things like .com and .net)

Long domains, the most notable ones are: