git-all-fetch.ps1

function Remove-MergedBranches
{
    Get-ChildItem -Recurse -Depth 2 -Force |
        Where-Object { $_.Mode -match "h" -and $_.FullName -like "*\.git" } |
        ForEach-Object {
            $dir = Get-Item (Join-Path $_.FullName "../")
            pushd $dir

            "removing merged branches in $($dir.Name)"
            git branch --merged | %{$_.trim()} | ?{$_ -notmatch 'develop' -and $_ -notmatch 'master'} | %{git branch -d $_}

            popd
        }
}

Remove-MergedBranches