The 1kb client side MV* library
Marko template engine
ComponentJS -- Powerful run-time Component System for structuring HTML5-based Rich Clients
Micro client-side router inspired by the Express router (~1200 bytes)
Making AJAX as easy as anchor tags
Ajax with less suck - (and node.js HTTP client to match)
A port of elm-effects and the Elm Architecture to Redux that allows you to sequence your effects naturally and purely by returning them from your reducers.
filter arrays using mongodb queries
Jade - robust, elegant, feature rich template engine for nodejs
Observable data. Reactive functions. Simple code.