Mono is an open-source implementation of the .NET framework (go-mono.org). It's primarily oriented toward .NET on Linux and OS X, and is backed by Novell and others.
Unfortunately, Mono does not yet implement all the features of .NET. Indeed, it has only certain minimal goals in its current pre-release status. BlueDragon needs features that it does not yet support, so BlueDragon does not currently run on MONO. We will be following its progress.