* Thin clients: everybody was going to have a 'dumb terminal', and all the computing/storage would happen elsewhere. There were many variations on this idea.
* PIMs: Palm Pilots and all the variations. I knew a guy who quit his job to develop Palm Pilot wares, claiming it was 'the future'. In a way, he was right.
* Windows: Linux was barely there, Unix was for neckbeards and universities, and it looked like Mac was mostly dead. It looked like Microsoft was about to swallow the world.
* The end of mice and keyboards: Yes, it sounds silly today. but supposedly VR/voice/whatever was going to replace it all.