Generates a `Directory.Packages.props` based on all your project files

ConvertTo-CentralPackageManagement.ps1

function ConvertTo-CentralPackageManagement() {
    Write-Host 'Searching for package references'

    $packages = @{}
    $conditionalPackages = @{}
    foreach ($csproj in (Get-ChildItem -Include *.csproj, *.props -Recurse)) {
        $root = [xml]($csproj | Get-Content -Raw)
        foreach ($itemGroup in $root.Project.ItemGroup) {
            foreach ($packageReference in $itemGroup.PackageReference) {
                if ($packageReference.Include -and $packageReference.Version) {
                    $packageName = $packageReference.Include
                    $packageVersion = $null
                    if (-not [System.Management.Automation.SemanticVersion]::TryParse($packageReference.Version, [ref] $packageVersion)) {
                        if (-not [System.Version]::TryParse($packageReference.Version, [ref] $packageVersion)) {
                            Write-Warning "Unable to parse version of $packageName"
                        }
                    }
                    if ($itemGroup.Condition) {
                        $packageCondition = $itemGroup.Condition -replace ' ', ''
                        if (-not $conditionalPackages[$packageCondition]) {
                            $conditionalPackages[$packageCondition] = @{}
                        }
                        if (-not $conditionalPackages[$packageCondition][$packageName] -or
                            $conditionalPackages[$packageCondition][$packageName] -lt $packageVersion) {
                            $conditionalPackages[$packageCondition][$packageName] = $packageVersion
                        }
                    } else {
                        if (-not $packages[$packageName] -or
                            $packages[$packageName] -lt $packageVersion) {
                            $packages[$packageName] = $packageVersion
                        }
                    }
                }
            }
        }
    }

    Write-Host "Found $($packages.Count) unique package references in all your projects"

    $xmlWriterSettings = [System.Xml.XmlWriterSettings]::new()
    $xmlWriterSettings.Indent = $true
    $xmlWriterSettings.IndentChars = '  '

    Write-Host "Writing package versions to: $pwd\Directory.Packages.props"

    $xmlWriter = [System.Xml.XmlWriter]::Create("$pwd\Directory.Packages.props", $xmlWriterSettings)
    try {
        $xmlWriter.WriteStartElement('Project')
        $xmlWriter.WriteStartElement('ItemGroup')
        foreach ($packageName in $packages.Keys | Sort-Object) {
            $xmlWriter.WriteStartElement('PackageVersion')
            $xmlWriter.WriteAttributeString('Include', $packageName)
            $xmlWriter.WriteAttributeString('Version', $packages[$packageName])
            $xmlWriter.WriteEndElement()
        }
        $xmlWriter.WriteEndElement()
        foreach ($packageCondition in $conditionalPackages.Keys | Sort-Object) {
            $xmlWriter.WriteStartElement('ItemGroup')
            $xmlWriter.WriteAttributeString('Condition', $packageCondition)
            foreach ($packageName in $conditionalPackages[$packageCondition].Keys | Sort-Object) {
                $xmlWriter.WriteStartElement('PackageVersion')
                if (-not $packages[$packageName]) {
                    $xmlWriter.WriteAttributeString('Include', $packageName)
                } else {
                    $xmlWriter.WriteAttributeString('Update', $packageName)
                }
                $xmlWriter.WriteAttributeString('Version', $conditionalPackages[$packageCondition][$packageName])
                $xmlWriter.WriteEndElement()
            }
            $xmlWriter.WriteEndElement()
        }
        $xmlWriter.Flush()
    } finally {
        $xmlWriter.Close()
    }

    Write-Host 'Removing version strings of package references from all your projects'

    Get-ChildItem -Include *.csproj, *.props -Recurse |
        ForEach-Object {
            $content = $_ | Get-Content -Raw
            $content = $content -replace '<PackageReference(.+?)\s+Version=".*?"', '<PackageReference$1'
            $content | Set-Content -Path $_.FullName -NoNewline
        }

    Write-Host 'Live long and prosper'
}

How is this not a built in thing already?!