How to use Paypal Sandbox?

What libraries (GDK, networking?) should I use for a sandbox-type game in C#?

• I’ve recently become enamored of C# when a friend told me that C# can be used very easily with Mono. I’ve been wanting to make a sandbox game in a minecraft-like vein, so I feel I’d need full C and not Java for its speed, but I am very worried about finding a decent networking layer for multi-player, as networking in C has historically been very poor. C# with Mono, or Unity, or XNA gives access to .NET for networking, and Mono and Unity are specifically aimed at game developers.  The friend who recommended this said it would be easy, and his coding skills are a bit lower than mine. For what I’d like to build, I want to have access down to the level of drawing polygons, i.e. I’d like to be down at the OpenGL level.  Higher-level things like particle-engines, imposed scenegraphs and other such things will annoy and impede me rather than help me. Note: Costs associated with development are not a problem.  Free and open-source are not constraints.

• Answer:

  Beware that Mono does not implement the entire .Net framework. If your game will be a commercial product, I'd recommend you to go to C++.