A refined 90s-style operating system you can actually use

SerenityOS (github) is "a love letter to '90s user interfaces with a custom Unix-like core", wedding the simplicity and style of Windows 9x with all the features (and security) you'd expect from a modern distribution. It's not intended to be accessible to normals ("this project does not cater to non-technical users") and I wouldn't hold out for amenities such as more legible fonts, etc. For lovers of aesthetics something like Chicago95 or the Redmond Project might be more approchable.