How can I reinstall Windows 10's calculator app?

This one worked for me, just combined the commands from the other answers found here. Note: you have to use the -Allusers option with the Get-AppxPackage command since it is not installed anymore under your current user account:

Get-AppxPackage -allusers *windowscalculator* | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)\AppXManifest.xml”}

Here is the MS Store link to the Windows Calculator.

Note: This will only work if you have the Windows Store app installed.

To reinstall an individual app use PowerShell and run it in admin mode. Screenshots:

Next get the full name of all apps, e.g. Windows Calculator paste this snippet in PowerShell and hit enter:

get-appxpackage -allusers | Select Name, PackageFullName

For single full name of the desired app name, e.g. Windows Calculator paste this snippet in PowerShell and hit enter:

Get-AppxPackage *windowscalculator*

Now copy the full name that looks like this: Microsoft.WindowsCalculator_10.1601.49020.0_x64__8wekyb3d8bbwe

Finally the we are going to install that app again with this snippet:

Add-AppxPackage -register "C:\Program Files\WindowsApps\Microsoft.WindowsAlarms_10.1603.12020.0_ x64__8wekyb3d8bbwe\appxmanifest.xml" -DisableDevelopmentMode

Re-installed app is available without restart of the PC!

N.b: To remove individual apps use this code: Get-AppxPackage *alarms* | Remove-AppxPackage

A list of all apps when removing is (Here)