Someone else may be better at explaining the differences than me, as neither are my area of expertise. My understanding is that they both provide a view layer,

Someone else may be better at explaining the differences than me, as neither are my area of expertise. My understanding is that they both provide a view layer, and Titanium provides more of an everything-included framework so you don't have to touch any native code. With React, it provides an easy to use view layer that helps you create compositions of components and layouts, but it's expected at some point you'll want/need to build things in native code. It's also expected that the overall architecture of the app to be provided by the developer. This gives more flexibility to break out of React or add it to existing projects where its helpful. Without having more experience with Titanium, its hard for me to say if you can use ReactNative along side it, but my gut says they probably have a different way of doing things.