The OpenNIC Project has established an alternate DNS network to resolve domain names to IP addresses, but it includes names not currently used by the internet. Available top-level domains include:

.geek
.indy
.bbs
.gopher
.o
.libre
.oss
.dyn
.null

You can register a domain within these (and more) top-level domains and register them on the OpenNIC DNS system so that they map to an IP address of your choice.

https://opensource.com/article/21/4/opennic-internet