Here is Windows 7 Metro start Orb pack, practically we can say it is an unofficial Windows 8 like start button collection.
The designer Bruellkaefer says:
I think Metro is the Design from Windows 8.
In this Pack is:
PNGs with transparent background to make your own thing
Windows 7 Start Orb Changer 2.6 for SP1 and old Windows version without updates
Windows 7 Start Orb Changer 4.0 for Windows version with Update but without SP1.
Windows 8 styled Metro start Orb pack