Just few days ago PowerShell Core 6.0 became general available. PowerShell Core 6.0 was engineered on the open source of the .Net core platform. It is cross-platform and you can run it on Windows, Linux or MacOS operating systems.
If you are looking to start using it, you can download the installation files here. It is compatible with Windows 7 and later OS. Because it is not the upgrade from the previous version, it will keep both versions together (5.1 and 6.0).
And if you would like to contribute, feel free to reach out the community.
Get all the details about the release from the Powershell Team Blog.