For some of these, you have to use them on the actual hardware to understand why so many of us are bummed about what we have lost. The latency of modern systems is kind of bonkers. Even though the machines were incredibly slow they feel faster than modern machines. Some musicians used Atari STs for years after they were discontinued because of the stable timing.

For others, the hardware wasn't important, but some of the functionality isn't apparent in a static screenshot. For example, I loved OS/2 and the Workplace Shell. It had functionality similar to Windows COM or CORBA in that everything on the system exposed an interface that could be easily scripted or used by other applications. The built-in scripting language was Rexx which I feel could have played the role Python does now if only OS/2 had taken off. Using OS/2 from 1.3 onwards felt like you were using a computer from the future.