Recently read about Oberon system and its compile speed, simplicity etc..
Finding out more about not-so-mainstream tech is one of the main reasons I read HN. And I see once in a while some "forgotten" tech mentioned, from where it seems the current state of art is a step back.
What's your favourite software / technology / tools that were better but couldn't make into mainstream?
IRC before Slack took off. IRC a standardized chat protocol, there is not chat islands.
Gopher, the text version of meta browsable Internet before World wide web. You could navigate gopher with just a keyboard. https://en.wikipedia.org/wiki/Gopher_%28protocol%29
BBS Bulletin Board systems there were local computer communities formed around them. https://en.wikipedia.org/wiki/Bulletin_board_system