NowJS is a framework for building realtime web apps (that doesn't do model synchronisation). Racer is real-time model synchronisation. Fundamentally they are

NowJS is a framework for building realtime web apps (that doesn't do model synchronisation). Racer is real-time model synchronisation. Fundamentally they are completely different. They happen to use similar technology stacks and both contain the word 'realtime' but they are completely different projects. They actually might work quite well as compliments to each other.