Windows PowerShell, previously Microsoft Shell or MSH (codenamed Monad) is an extensible command line interface (CLI) shell and scripting language product developed by Microsoft. The product is based on object-oriented programming and the Microsoft .NET framework.
Windows PowerShell 1.0 is available for download from the Microsoft web site.
At work I've been playing with Windows PowerShell. I could try to describe it, but Wikipedia has already done a better job:
It blows my mind how cool it is. Unfortunately it also, uhh, fries my brain because I don't know how to use it. I'm a cmd.exe expert. Seriously, I know way, way too much about writing CMD scripts, to the point where most people can't keep up. I don't want this knowledge, and I see that PowerShell may give me freedom from the burden of the knowledge.
My biggest annoyance is that it's not universally available. I want to be able to sit down at any machine and just start using PowerShell, not having to worry about installing it (and the .Net Framework) first. I want to be able to offer .PS1 scripts for anyone to use, without them having to jump through the same hoops.
Too bad it missed the Vista train. That means it'll be 10 years before it's everywhere. We'll get there.