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Well their promise not to sue is in written form and on "alternative" platforms I will avoid the System.Windows namespace like the plague (since that part is not included in their license). That is good enough for me and I choose to be an opportunist.
C#? Your Mac port is already toast. You'll either have to wrangle the Mono framework as a built-in dependency or convince your users to install it for system-wide use. Good luck with that.
The situation is a lot less dire on Linux, where GNOME flirted with Mono for a long time before Vala showed up, but you'll still need to check dependencies.
Your best bet would be to rewrite the core/server code in C, or at least in a language that compiles to C and exports C APIs (only Vala comes to mind). Of course, then you have to worry about the fact that each environment does audio differently.... Come to think of it, this is a very silly project. Edited 2012-01-24 22:42 UTC