MonoMac is an open source library for building Cocoa applications on Mac OS X using Mono.
MonoMac: an open-source foundation for building Cocoa applications on OSX using Mono.
MonoMac is the result of years of experimentation in blending .NET with Objective-C and is inspired by the same design principles that we used for MonoTouch.
It is also the result of weekend hacking as our day to day work revolves around Mono's efforts on Linux servers, Linux desktops, Visual Studio integration and our mobile efforts. Luckily, it shares some components with MonoTouch.
A new commercially supported offering, Xamarin.Mac, is a superset of MonoMac and include a license to deploy the Mono runtime (without the LGPL requirements).