If you are still using Windows 7, there is a good chance that you are using 'Aero Glass'. The theme has been widely popular among enthusiasts over the years, and if you are running Windows 10, you will soon have the option to turn this theme back on.
The folks over at Glass8.eu
are working diligently to release the tools needed to enable the theme. While their website makes it seem like the release of the files needed to enable the theme are not going to be available anytime soon, a post by the creator on MDL
states that because there are "no large changes in Win10's DWM, you can expect Aero Glass for Win10 earlier than" previously expected.