The .alt Special-Use Top-Level Domain(rfc-editor.org)
rfc-editor.org
The .alt Special-Use Top-Level Domain
https://www.rfc-editor.org/rfc/rfc9476.html
2 comments
We use this SU-TLD in our GNS draft which is also already in the editor queue: https://datatracker.ietf.org/doc/draft-schanzen-gns/
Many many years ago (late 90s) I used to use ".l" (dot ell), nominally meaning 'local', for this purpose, on the assumption that a legit single letter TLD wasn't happening any time soon, and it was visually distinctive.