>>305418303
The old project from the OVRDrop dev supposedly works on 7. The Windows 7 screen capture API is slow and I have no idea if the overlay still works with newer version of Steam VR, but it's free, so no harm in trying I guess.
https://github.com/Hotrian/OpenVRDesktopDisplayPortal
Also, OVRDrop supposedly works on Windows 8 if you're on that.