I'd like to raise some awareness of a medium that most of you probably have never heard of. It's the Videotex set of online services in Europe.
Those services were available in different countries under different names and in different technical variants:
In the UK it was called "Viewdata" and had a very basic set of features.
The French "Minitel" was the most successful of these services with a bit more features.
"Bildschirmtext" in Germany had more colours and user definable character sets. (those can be seen in the attachments)
Those services were roughly related to Teletext, but were transmitted via the telephone line.
Some terminals had a connection for tape decks and this is how some of the content survived. Typically those were recorded with V.23 modem encoded data. This can be recognized by having an idle tone of 1300 Hz.
So far the loose group I'm a member of only found a tiny amount of the pages that existed. They can be found in this repository:
BTW I recently got a set of 63 tape cassettes containing Bildschirmtext pages from a company producing those. I'm currently trying to decode those. If you want to help (particularly in categorizing those pages), feel free to contact me. They are mostly from Insurance companies as well as lots of internal pages from the company Standard Elektrik Lorenz SEL.