Windows 95 as an Electron App
An operating system that was released 25 years ago and required an entire computer to run can now instead be run in a browser window with an interpreted language.
Retro Software: BeOS
In the early-1990s, a lesser-known operating system was born named BeOS. It was an operating system that was ahead of its time, but was never able to gather much support.
Emulating Mac OS 9 on macOS 10.15
Several years ago, I bought an old, colorful iMac G3 running Mac OS 9. It runs my old software wonderfully, but an emulated version of Mac OS 9 on my modern MacBook Pro is just so much more convenient.