PowerShell is the closest of Xerox PARC REPL experience that ships in the box on modern platforms.
Because not only it is a proper programming language, it is integrated into .NET, COM/DLLs as well, so not only you can script the OS, any application automation library is exposed as well.
Nowadays, it is possible to automate anything on Windows via PowerShell, the same OS APIs exposed by GUIs are also accessible to PowerShell.
On UNIX side there are things like Fish shell that also offer these capabilities, but they aren't widely adopted as PowerShell on Windows.
Sorry, but Powershell is not a programming language. It has way too many quirks and gotchas to qualify as a programming language. It is an interactive scripting language first, and a scripted language second. But a programming language it is not.
To give just one example: its automatic boxing and unboxing of arrays disqualifies it as a programming language. Try to return a one-element array from a Powershell function and you'll see what I mean.
Because not only it is a proper programming language, it is integrated into .NET, COM/DLLs as well, so not only you can script the OS, any application automation library is exposed as well.
Nowadays, it is possible to automate anything on Windows via PowerShell, the same OS APIs exposed by GUIs are also accessible to PowerShell.
On UNIX side there are things like Fish shell that also offer these capabilities, but they aren't widely adopted as PowerShell on Windows.