The Pash-Project is an Open Source reimplementation of Windows PowerShell on Mono.

Due to the size/scope of PowerShell itself, Pash has a long ways to go. However you may be surprised at how active some contributors to the project are and how useful the project can actually be in certain contexts.

Resources

Project Status

Travis-CI: Linux Build Status (Travis-CI) - Linux builds
AppVeyor: Windows Build Status (AppVeyor) - Windows builds
Pull Request Stats