There are a few options available, to name a few:
Three.js an open source library hosted on GitHub with examples and fairly good documentation.
O3D created by Google with not a lot of documentation or examples.
CopperLicht has fairly well documented site with a few example but you are required to download CopperCube (being the development area) which you have to pay for after 14 days.
Finally StormEngineC which has various examples and some decent documentation.