PowerShell script to return versions of .NET Framework on a machine?

If you're going to use the registry you have to recurse in order to get the full version for the 4.x Framework. The earlier answers both return the root number on my system for .NET 3.0 (where the WCF and WPF numbers, which are nested under 3.0, are higher -- I can't explain that), and fail to return anything for 4.0 ...

EDIT: For .Net 4.5 and up, this changed slightly again, so there's now a nice MSDN article here explaining how to convert the Release value to a .Net version number, it's a total train wreck :-(

This looks right to me (note that it outputs separate version numbers for WCF & WPF on 3.0. I don't know what that's about). It also outputs both Client and Full on 4.0 (if you have them both installed):

Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -recurse |
Get-ItemProperty -name Version,Release -EA 0 |
Where { $_.PSChildName -match '^(?!S)\p{L}'} |
Select PSChildName, Version, Release

Based on the MSDN article, you could build a lookup table and return the marketing product version number for releases after 4.5:

$Lookup = @{
    378389 = [version]'4.5'
    378675 = [version]'4.5.1'
    378758 = [version]'4.5.1'
    379893 = [version]'4.5.2'
    393295 = [version]'4.6'
    393297 = [version]'4.6'
    394254 = [version]'4.6.1'
    394271 = [version]'4.6.1'
    394802 = [version]'4.6.2'
    394806 = [version]'4.6.2'
    460798 = [version]'4.7'
    460805 = [version]'4.7'
    461308 = [version]'4.7.1'
    461310 = [version]'4.7.1'
    461808 = [version]'4.7.2'
    461814 = [version]'4.7.2'
    528040 = [version]'4.8'
    528049 = [version]'4.8'
}

# For One True framework (latest .NET 4x), change the Where-Object match 
# to PSChildName -eq "Full":
Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -Recurse |
  Get-ItemProperty -name Version, Release -EA 0 |
  Where-Object { $_.PSChildName -match '^(?!S)\p{L}'} |
  Select-Object @{name = ".NET Framework"; expression = {$_.PSChildName}}, 
@{name = "Product"; expression = {$Lookup[$_.Release]}}, 
Version, Release

In fact, since I keep having to update this answer, here's a script to generate the script above (with a little extra) from the markdown source for that web page. This will probably break at some point, so I'm keeping the current copy above.

# Get the text from github
$url = "https://raw.githubusercontent.com/dotnet/docs/master/docs/framework/migration-guide/how-to-determine-which-versions-are-installed.md"
$md = Invoke-WebRequest $url -UseBasicParsing
$OFS = "`n"
# Replace the weird text in the tables, and the padding
# Then trim the | off the front and end of lines
$map = $md -split "`n" -replace " installed [^|]+" -replace "\s+\|" -replace "\|$" |
    # Then we can build the table by looking for unique lines that start with ".NET Framework"
    Select-String "^.NET" | Select-Object -Unique |
    # And flip it so it's key = value
    # And convert ".NET FRAMEWORK 4.5.2" to  [version]4.5.2
    ForEach-Object { 
        [version]$v, [int]$k = $_ -replace "\.NET Framework " -split "\|"
        "    $k = [version]'$v'"
    }

# And output the whole script
@"
`$Lookup = @{
$map
}

# For extra effect we could get the Windows 10 OS version and build release id:
try {
    `$WinRelease, `$WinVer = Get-ItemPropertyValue "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion" ReleaseId, CurrentMajorVersionNumber, CurrentMinorVersionNumber, CurrentBuildNumber, UBR
    `$WindowsVersion = "`$(`$WinVer -join '.') (`$WinRelease)"
} catch {
    `$WindowsVersion = [System.Environment]::OSVersion.Version
}

Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -Recurse |
    Get-ItemProperty -name Version, Release -EA 0 |
    # For The One True framework (latest .NET 4x), change match to PSChildName -eq "Full":
    Where-Object { `$_.PSChildName -match '^(?!S)\p{L}'} |
    Select-Object @{name = ".NET Framework"; expression = {`$_.PSChildName}}, 
                @{name = "Product"; expression = {`$Lookup[`$_.Release]}}, 
                Version, Release,
    # Some OPTIONAL extra output: PSComputerName and WindowsVersion
    # The Computer name, so output from local machines will match remote machines:
    @{ name = "PSComputerName"; expression = {`$Env:Computername}},
    # The Windows Version (works on Windows 10, at least):
    @{ name = "WindowsVersion"; expression = { `$WindowsVersion }}
"@

Added v4.8 support to the script:

Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -recurse |
Get-ItemProperty -name Version,Release -EA 0 |
Where { $_.PSChildName -match '^(?![SW])\p{L}'} |
Select PSChildName, Version, Release, @{
  name="Product"
  expression={
      switch -regex ($_.Release) {
        "378389" { [Version]"4.5" }
        "378675|378758" { [Version]"4.5.1" }
        "379893" { [Version]"4.5.2" }
        "393295|393297" { [Version]"4.6" }
        "394254|394271" { [Version]"4.6.1" }
        "394802|394806" { [Version]"4.6.2" }
        "460798|460805" { [Version]"4.7" }
        "461308|461310" { [Version]"4.7.1" }
        "461808|461814" { [Version]"4.7.2" }
        "528040|528049" { [Version]"4.8" }
        {$_ -gt 528049} { [Version]"Undocumented version (> 4.8), please update script" }
      }
    }
}