Rajawali is an free open source 3D library for Android which I created. It is not a cross-platform offering but specifically designed for Android. Creating 3D content is made easy by abstracting all the low-level details which means developers can be more effective and focus on being creative.
Rajawali has specific bindings for augmented reality, virtual reality and Android Wear. Recently Google integrated Rajawali into their official Project Tango Java SDK, a Google technology platform that uses computer vision to enable mobile devices, such as smartphones and tablets, to detect their position relative to the world around them without using GPS or other external signals.
Examples of apps, games and live wallpapers that have been built using Rajawali can be found on the Rajawali Google+ page.