PowerShell is a scripting language with an accompanying command-line shell created by Microsoft to automate tasks on Windows. PowerShell has a strong focus on system administrators. PowerShell has the .NET framework at its core, and hence brings all the features and the excellent library support to system administration activities.
PowerShell is not just for system administrators. It is for developers too. To stress this point, there is even a book called Windows PowerShell for Developers, Douglas Finke, O'Reilly Media.
With a strong scripting language powered by the .NET framework and its focus on automating tasks, PowerShell makes for a good platform for creating build tools.