You can build a realtime data push service using Node.JS and Socket.IO and manage it yourself, scale it (with a lot of effort), etc. In contrast, PubNub provides this capability (plus many advanced features) as a network service and simple-to-learn APIs in > 70 SDKs for web, mobile, desktop, server and embedded platforms, all maintained in-house as free and open source under an MIT license.
PubNub infrastructure spans 15 data centers and that immense capacity is provided on a pay-as-you-go basis so that developers can start small with no upfront infrastructure costs.
That's why PubNub has been chosen by thousands of startups, SMBs and large companies to power their web, server, mobile and embedded device apps' realtime data stream network needs. Whether it is IoT (connected cars, dispatch service, home automation, iBeacons, Arduinos, Raspberry Pi), social interaction, business collaboration, Voice-over-IP (VoIP) or broadcasting special entertainment and sports events, PubNub is commonly used in the Node.JS/Socket.IO environment to provide scalable deployment capabilities.