Horizon vs PubNub: What are the differences?
Developers describe Horizon as "*A realtime, open-source JavaScript back end from RethinkDB *". Horizon provides a complete backend that makes it dramatically simpler to build, deploy, manage, and scale engaging JavaScript web and mobile apps. Horizon is extensible, integrates with the Node.js stack, and allows building modern, arbitrarily complex applications. On the other hand, PubNub is detailed as "Build real-time apps quickly and scale them globally". PubNub makes it easy for you to add real-time capabilities to your apps, without worrying about the infrastructure. Build apps that allow your users to engage in real-time across mobile, browser, desktop and server.
Horizon and PubNub can be categorized as "Realtime Backend / API" tools.
Horizon is an open source tool with 6.77K GitHub stars and 389 GitHub forks. Here's a link to Horizon's open source repository on GitHub.