This was inspired by fishtown's Simple Raspberry Pi Mount but does not require to screw in the Raspberry. I needed this to fit it on a Raspberry with a HyperPixel 4 display which uses the Raspberry Mount holes for attaching the display.
The mount should fit the Raspberry Pi B+ and Raspberry Pi 3. Simply slide the GPIO side under the small lip, then gently press the PCB into the rim.
You can either screw it down using the holes in the mount frame or use my Hook for Rasperry Pi Mount.
OpenSCAD sources available at Github