Ribbon interface for GTK and Qt

Yes, some libraries for Ribbon widgets have already been released.

_{see this post and this one.}

There is also QtitanRibbon, an implementation of Microsoft's Ribbon UI for QT.

I don't have enough rep to vote or comment, but @Daniele Lupo's comment about needing to sign an agreement isn't quite true. There is enough prior art floating around that suggests Microsoft won't be awarded the patent.

Source: Ribbon (computing)