The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++. It is completely cross-platform, using D3D, OpenGL and its own software renderers.
Icarus Scene Engine is a cross-platform, CLS-compliant 3D framework, integrating open source APIs into a cohesive all-open-source, all .NET solution. For Windows, MacOSX & Linux.
Uses OpenTK, OpenGL, OpenAL APIs for graphics and audio. Runs on Mono/.NET. Links to FFMpeg for streaming video, and FreeType as a temporary conversion mod to bring fonts into a native XML format.
A cross-platform game framework based on OpenGL and GObject.
MaxDream is a cross-platform open source game(/simulation) framework based on OpenGL and GObject.
MaxDream aims to be compatible with any game techniques, so you can use MaxDream, without changing your OpenGL methodology.
Open-source, cross-platform 3D rendering engine for .NET and Mono. The Axiom Engine is a high-performance C# port of the powerful OGRE engine and provides full support for DirectX, OpenGL and XNA on Windows, Linux, Android, iPhone and Windows Phone.
Irrlicht .NET CP is a .NET wrapper of the famous Irrlicht rendering engine. It provides a full, entirely cross-platform 3d rendering engine working with any .NET language. Moreover it has an extensions library which adds a lot of features to the engine.
A cross-platform terrain rendering engine that uses advanced techniques such as dynamic tessellation to render complex landscapes at high frame rates. Suitable for use in games, engineering, simulation, etc.
Cross-platform C# OpenGL .NET Winform Control. waglx allows to use OpenGL on a WinForm Control without knowledge in operating systems OpenGL initializations. The waglx applications can be run from the same binary on any platform using Mono.
Intended to be a cross-platform 3D engine and toolkit using the Tao framework and allowing C#/F#/.NET developers to target Mac OS X and Windows with a single build.
Also includes accessory tools for managing builds and ports of your game product.