PowerShell SharePoint Module Get all installed features on a site collection
Example
Get-SPFeature -Site https://mysharepointsite/sites/test
Get-SPFeature can also be run on web scope (-Web <WebUrl>), farm scope (-Farm) and web application scope (-WebApplication <WebAppUrl>).
Get all orphaned features on a site collection
Another usage of Get-SPFeature can be to find all features that have no scope:
Get-SPFeature -Site https://mysharepointsite/sites/test |? { $_.Scope -eq $null )
