Go Pro Hero 4 hotshoe skeleton case.

thingiverse

UPDATE: new version holds better, has multiple angles you can mount with (vertical as well) and is stronger. it fits like a glove if you have a printer that can print good dimensions. print it slow and how, I used petg. the little notches bend upwards a bit when putting the camera in and then hold it secure. the hotshoe mount part fits on most modern cameras.