A PowerShell prompt function using a synchronized hashtable and runspace to display server status (up/down).

UpDownPrompt.ps1

function prompt {

    $up = 0x25b2 -as [char]
    $down = 0x25bc -as [char]

    Try {
        Get-Variable -Name testHash -Scope global -ErrorAction Stop | Out-Null
    }
    catch {
         #create the runspace and synchronized hashtable
        $global:testHash = [hashtable]::Synchronized(@{Computername = $env:computername;results = ""; date= (Get-Date)})
        $newRunspace = [runspacefactory]::CreateRunspace()
        #set apartment state if available
        if ($newRunspace.ApartmentState) {
            $newRunspace.ApartmentState = "STA"
        }
        $newRunspace.ThreadOptions = "ReuseThread"         
        $newRunspace.Open()
        $newRunspace.SessionStateProxy.SetVariable("testHash", $testHash)  

        $pscmd = [PowerShell]::Create().AddScript( {  
                #define the list of computers to test
                $computers = "dom1", "srv1", "srv2", "srv3"

                do {
                    $results = $computers | ForEach-Object {
                        [pscustomobject]@{
                            Computername = $_.toupper()
                            Responding   = Test-WSMan -ComputerName $_
                        }
                    }

                    $global:testHash.results = $results
                    $global:testHash.date = Get-Date
                    #set a sleep interval between tests
                    Start-Sleep -Seconds 5
                } while ($True)

            })

        $pscmd.runspace = $newrunspace
        [void]$psCmd.BeginInvoke()

    } #catch
    Write-Host "[" -NoNewline

    $global:testHash.results.foreach( {
            Write-Host $_.Computername -NoNewline
            if ($_.responding) {
                Write-Host $up -ForegroundColor green -NoNewline
            }
            else {
                Write-Host $down -ForegroundColor red -NoNewline
            }
        })

    Write-Host "]" -NoNewline

    "PS $($executionContext.SessionState.Path.CurrentLocation)$('>' * ($nestedPromptLevel + 1)) "

}

This function is described at https://jdhitsolutions.com/blog/powershell/6275/powershell-updown-prompt/