Question: What does AAPT (Android Asset Packaging Tool) mean? How does it work?

Can I ship the `.so` file of one application in the APK file of another application using AAPT?

Answer: 
AAPT allows you to view, create, and update ZIP-compatible archives (ZIP, JAR, and APK). It can also compile resources into binary assets. It is the base builder for Android applications.

Of course you can ship .so files from an application, but if you want to use it, you will need reverse engineering plugins and these are not very recommended because of the complexity. I don't know anyone for Android, but there are a bunch of environments plugins.

Also you can research a bit before posting,

* [AAPT usages](http://elinux.org/Android_aapt)
* [Reverse engineering for Android](https://reverseengineering.stackexchange.com/questions/4624/how-do-i-reverse-engineer-so-files-found-in-android-apks)
When your application is compiled, AAPT generates the R class, which contains resource IDs for all the resources in your `res/` directory. For each type of resource, there is an R subclass (for example, R.drawable for all drawable resources), and for each resource of that type, there is a static integer (for example, R.drawable.icon). This integer is the resource ID that you can use to retrieve your resource. 

SOURCE: <https://developer.android.com/guide/topics/resources/accessing-resources.html> (copy/pasted)