"The goal of ANGLE is to allow Windows users to seamlessly run WebGL and other OpenGL ES 2.0 content by translating OpenGL ES 2.0 API calls to DirectX 9 or DirectX 11 API calls."
These are required if you wish to publish an OpenGL ES application to the Windows Store. You can also use these in order to port or test OpenGL ES code from and to mobile devices (Android, iPhone).
[monolinker]
Mono Linker project. Use this to reduce the size of OpenTK.dll.
http://www.mono-project.com/Linker
"The linker is a tool one can use to only ship the minimal possible set of functions that a set of programs might require to run as opposed to the full libraries."
where "YourApplication.exe" is the name of your application binary. This command will create a new folder "output/" with a copy of your application and optimized version of OpenTK.dll and any other dll your application is using.