Backbone is really just an event bus, some smart wrapper logic around updating an object and an array, and a nicer setup syntax for jQuery event handlers for a particular element tree. People have then built addons that handle relational models, derived data, view lifecycles, and so on.

Redux is just putting all/most your data in a single "model", making sure all writes happen explicitly and immutably, and firing a single "change"-like event. From there people have built various ways of organizing side effects, listening for specific changes, and hooking into other libraries.

So, both simple libraries that form the basis for an ecosystem, and let you pick-and-choose the pieces that you specifically need.