Dash 4 is an app that allows you to manage snippets of code and look up API (application-program interface) documentation, whether you're at home or on the go. It stores API 'docsets' for more than 150 programming languages, and it allows you to search them whether you're online or offline. This makes it a good tool for learning to program, for remembering what a given function does, or even just for organizing many stray bits of code.
A Development Aid, Not A Development Environment
Dash 4 allows you to store snippets of code, search them, and search API docsets to know what every function in a code snippet does. This makes it a powerful tool for analysing unfamiliar code or untangling code that you personally wrote a long time ago. However, the interface is not built to store and search large chunks of code, just snippets. It also provides few syntactical aids, making it hard to write code from scratch. But that's not what the app is for. It searches docsets quickly and efficiently, and it runs well in all of its version.
Well-Designed But Simple
Overall, Dash 4 is great to have in your back pocket if you've just learned the basics of programming or if you feel you need it to keep on top of a complex API. It works well for what it's meant to do.