It's a way of using Windows that is very tolerable to POSIX commandline diehards. The similarities are numerous and include enhanced scriptability and even small details like up-arrow command history. You could get all of that with Cygwin, but Powershell adds tight OS integration, access to COM objects (or whatever we're calling them this year) as well as the remoting of objects. It's a useful and powerful shell that reminds me of VMS DCL and csh.