Enumerate Windows URI Handlers (Keys in HKEY_CLASSES_ROOT that contain "URL Protocol" values), examples: http:, calculator:, ms-officecmd:

Enumerate-URIHandlers.ps1

New-PSDrive -Name HKCR -PSProvider Registry -Root HKEY_CLASSES_ROOT -ErrorAction SilentlyContinue | Out-Null
$count = 0
try {
    Get-ChildItem HKCR:  -ErrorAction SilentlyContinue | ForEach-Object {
        if((Get-ItemProperty $_.PSPath -ErrorAction SilentlyContinue).PSObject.Properties.Name -contains "URL Protocol") {
            $name = $_.PSChildName
            $count += 1
            $line = "URI Handler {0:d4}:   {1}" -f $count, $name
            Write-Host $line
        }
    } 
}
catch {}