What are some alternatives?
When comparing twitter.github.io Kestrel and Firebase, you can also consider the following products
nginx - A high performance free open source web server powering busiest sites on the Internet.
Android Studio - Android development environment based on IntelliJ IDEA
CloudAMQP - CloudAMQP automates every part of setup, running and scaling of RabbitMQ clusters. Available on all major cloud and application platforms.
Xcode - Xcode 4 is the new version of Apple’s powerful integrated development environment for creating great apps for Mac, iPhone, and iPad. Xcode 4 includes the Xcode IDE, instruments, iOS Simulator, and the latest Mac OS X and iOS SDKs.
RabbitMQ - RabbitMQ is an open source message broker software.
PubNub - PubNub is a real-time messaging system for web and mobile apps that can handle API for all platforms and push messages to any device anywhere in the world in a fraction of a second without having to worry about proxies, firewalls or mobile drop-offs.