Bent from Fuse here: I wouldn't say so. Xamarin strikes us as something meant for people who want to code C# and work within the .NET ecosystem, while Fuse takes a completely different approach (to both how you develop your apps, and what you spend your time on while doing it). The choice of JS for business logic was also made to enable more people to find an easier path into app development. Our UX Markup (that compiles to native C++ code) is one thing that makes Fuse differ quite a lot from many other frameworks.