OpenTK 

The Open Toolkit is an advanced, low-level C# library that wraps OpenGL, OpenCL and OpenAL. It is suitable for games, scientific applications and any other project that requires 3d graphics, audio or compute functionality.

Main features:

- Rich, type-safe bindings

- Support for the latest versions of OpenGL, OpenGL|ES, OpenAL and OpenCL with automatic extension loading, error checking and inline documentation.

- Flexible GUI options

- Cross-platform GLControl (Windows.Forms), GLWidget (GTK#) and WPFControl classes. Native, high-performance GameWindow designed specifically for games.

- Fully managed, CLS-compliant code

- Supports 32- and 64-bit versions of Windows, Linux and Mac OS X. No need for unmanaged libraries - compile once, run everywhere!

- Useful APIs

- 3D math toolkit supplies Vector, Matrix, Quaternion and Bezier structs. Input API provides Keyboard, Mouse and Joystick interfaces. Display API for multiple monitors. OpenTK.Compatibility supports Tao framework applications.

- Permissive MIT/X11 License

- Which means you are free to use, modify and redistribute the source code. Suitable for open- and closed-source projects alike.