Libraries/API Wrappers:

This API documents the HTTP calls from GoPro cameras, users have made libraries for several languages for convenience.

Ruby:

konradit/gopro-rb-api - Ruby API for GoPro HERO4/5

NodeJS/NPM:

kschzt/gopro - provides a Node.js API for HERO3 cameras
citolen/goproh4 - Node.js API for HERO4 cameras, available in NPM

Python:

Konradit/gopro-py-api - Python library for GoPro HERO3/3+/H4/H5/HERO+ cameras
joshvillbrandt/goprohero - Python library for GoPro H3/H3+/H4 cameras
DenisCarriere/gopro - Python library for HERO4/5 cameras

Java:

topiltzin-butron/gopro - Java API for GoPro HERO3+
konradit/gpApi - Java API for HERO3/3+/4/5

C Sharp:

r1pper/GoPro.Hero - C# Library for HERO2/HERO3/HERO4

GoLang:

coming soon