One difference is that there is no need to explicitly subscribe to signals. For general functions, knockout requires manually declaring "myViewModel.property.subscribe(...)" for each model you need to subscribe to. In contrast, Reactor's observer blocks automatically detect which signals you have read and sets up the subscriptions automatically.

Knockout has a different class for ko.computed vs ko.observable. For Reactor you use "Signal" for both and just pass in a function when its computed. Additionally there is no need for the trailing "this" at the end of ko.computed.