Here at GitHub, we're always excited to see people using GitHub to collaborate on all sorts of things, code or non-code. Today, we're adding a third dimension by making it easier to view some 3D models, specifically STL files, on GitHub.
You're able to spin the model by clicking & dragging, zoom in/out by scrolling, and change the view modes with the links at the bottom. This viewer is powered by Three.js and uses WebGL when available, but will fall back to the slower canvas renderer. If you have further questions, check out the help article.