MLVWM - Macintosh Like Virtual Window Manager
This window manager emulates System Software 7/Mac OS 8/9, its source is available from GitHub https://github.com/morgant/mlvwm/ also as binary for Arch-like distros (via AUR), NixOS, OpenBSD Ports, pkgsrc, Fedora (via RPM Sphere). It is recommended to copy configuration file - mlvwmrc to $HOME as it contains configuration of applications.

Stolen screenshot
Progman
This window manager emulates progman.exe of Windows 3.1. Source is available from GitHub https://github.com/jcs/progman, dependencies are X sources and gdk-pixbuf-xlib. As binary it is available for Fedora, pkgsrc, T/2 and EPEL. It is very helpful to copy progman.ini from source to ~/.config/progman/.

This screenshot is also stolen