Android Arsenal - As a mobile developer, sometimes it’s hard to find libraries for a feature you need in your application without tons of Googling. Android Arsenal simplifies that process. There are over a thousand free categorized libraries linked on the site, so whatever you need is easy to find.
Cocoa Pods - If you’re an iOS developer, you definitely should use Cocoa Pods for handling the libraries you’re using for your app. Why? Instead of downloading a library, dragging all the files into your project, and making sure all the files are imported correctly - Cocoa Pods allows you to add a library to your project just by adding one line of code to your Podfile.
Picasso - Do you need to download pictures from the internet in your app? Picasso is an Android library that allows you to easily show pictures from the internet in your app as long as you have an image link. The great part is, it will cache the images for the user so they don’t have to see the image re-downloading every time.
AFNetworking - AFNetworking is an iOS library that allows you to easily integrate any networking needs in your app, i.e GET or POST requests, URL handling, downloading images, etc. Although iOS has some built in networking capabilities, AFNetworking is simplier and more powerful.
App Annie - When you launch your application on the iTunes App Store or Google Play Store, you probably want to see how well it’s doing. That’s what App Annie is for. App Annie gives you all the analytical data on your app’s downloads, monetization, usage, and rankings. They have a free model as well as monthly rates that depend on how much tracking you need for your app. It’s important to keep up with your application and see how it fares in the store, especially as you add new releases. This will help you see all the data in one place.