That isn't trivial as some features are specific to SQL the server product while others are client (libraries and shared components). There isn't a reliable way to get the features that were installed as part of a SQL installation. Some of them may have been installed before or after SQL.
If you want to focus in on SQL services only and/or find the other things that were installed (from SQL or otherwise) then you have to use WMI and querying. Here's a SO post that will help get you started.