The oldest domain is still going strong http://nordu.net NORDUnet is a collaboration between the National Research and Education Networks (NRENs) of the five Nordic countries; Denmark (DeIC), Iceland (RHnet), Norway (UNINETT), Sweden (SUNET), and Finland (Funet). The Nordic region (five countries and three autonomous areas) has a population of 25 million, 9 official languages, and a strong tradition of collaboration.…
Well NORDUnet has been first with a lot of things, like the first DNS server outside the US, and the first IP router in Europe see: https://www.nordu.net/content/history-nordunet.