FVWM

Robert Nation, who also wrote the rxvt terminal, built FVWM in 1993 on top of the twm code base. The goal was to use less memory than the alternatives at a time when eight megabytes was a lot. What the F stands for has never been officially settled; the project itself has offered several suggestions.

FVWM's pager, a little map of all your virtual desktops, made the idea familiar to plenty of Unix users. Everything lives in a text file where menus, key bindings and window behaviour can be rewritten from scratch, and the FVWM95 variant proved in 1995 that with enough patience it could be made to look like Windows. AfterStep started as a fork. FVWM is still alive, at version 3 since 2020.