The real competition to Backbone in this space in my mind is Sproutcore 2. At its core it's lightweight enough to be a drop-in replacement but has a vastly more

The real competition to Backbone in this space in my mind is Sproutcore 2. At its core it's lightweight enough to be a drop-in replacement but has a vastly more sophisticated approach to handling dom updates, cascades of updates, data bindings and dealing with large sets of data.