Program Manager was the default shell for Windows (NT) 3.x. The Program Manager shell was included as an optional component in Windows until Windows 2000. It contained a basic task manager, a group-based program launcher and a shutdown dialog.
Program Manager II is a shell designed to supercede the original Microsoft Program Manager with better compatibility, stability, and usability. It's currently in alpha and doesn't contain all of the necessary functionality, but progress is being made.
Program Manager II will run on Windows Vista and above with no problem. Support for XP and older is not guaranteed, nor will it be ported to 9x.
The releases page will contain the latest "stable" version of Program Manager II. Build artifacts can be found for most commits made since April and contain pre-release builds.
You can look through all of the issues in the issue tracker with the Beta milestone attached to them to see what's planned. Otherwise, you can message me, 'freedom_usa' on Discord and ask about the direction of the project after feature parity is reached.
Submitting issues with bug reports, suggestions or comments always helps. If you're able to, contributing with a pull request is much appreciated.