@sally @HopperMCS @Yoruka @Zergling_man @meso @rher GNU still offers the latest version of the free DotGNU, but you have no hope getting anything to compile not specifically written for DotGNU.

The GPLv2 does have exceptions that allow for free software even written in proprietary languages, but there could be some issue with C# when it comes to the library bindings - I'm not sure if the GPLv2's system library exception would apply to those bindings if they are proprietary.