Every operating system have its own software package that are programmed to work only in thier operating system due to thier hardware and software working module like windows have .exe and iOS have .ipa this packages won't work in any other operating systems except them and same goes for android which is based on linux and has its own package .apk which have huge popularity due to its worldwide usage. 

A package contains a program that should be compatible with operating system then only the package is executable either to install or run for various purposes. 

The program that a package may contain a lot of different programming languages or a single program based on the project like  . exe use c, c++, . ipa use swift and .apk use java programming languages. 

Today, dev's using alot of programming languages to create single package except apple swift due to it's closed source other than that all the remaining open source programming languages are been utilised combinely to create single package by developers to make it work as they want according to thier project.

Every programming language have its own prospects and cons according to that they have to utilise this open source languages like C programming is high level language that can be used on any operating system available today or python is good if you are making any artificial intelligence project or java is best for mobile software's and java- script used to develop web based apps or progressive web apps for today's modern world technology's. 

Now, you know what is package and how it it is developed to work in operating system well it's is just beginning let's dive into .apk package will find out what is in .apk.

A .apk is a software package that is only developed to work on android operating system like apple's iOS or windows .exe the .apk can't be installed directly in any other os except android os developed by google or can able to run in windows with android emulator or android SDK to test apps. 

In .apk package it is just not an .extension as we earlier said it contains a executable program to work in operating system that program can be edited, modify or delete according to your requirements. 

But, a package can't be edited, modify or delete without a manager or viewer that is developed to open this packages. 

We have numerous managers available to read or write in windows but in android we doesn't have powerful package viewer that can edit or modify or delete the files that a package parsed.

In detailed a  .apk package like any other packages out there contains a different type of programming languages, mainly these things are important like package name, package version, SDK version level, android manifest, images, files, hidden code, trackers, permissions required, and all necessary things. 

Once, .apk package is perfect without any errors then it can installed in android with the help of package installer available in operating system that verify is everything that a package contains is ok or not if it is ok then it can installed or else you get any error message like can't install app etc. 

We are now familiar with .apk package and it's working structure but wait you can edit this important things with a basic level apk editor or a file editor available in file man - ager made for android. 

However, Android got alot of great dev's who done alot of hard work to control any type of files in .apk package merging alot of things into single app. 

Yes, a developer named muntashir 
al-Islam made such a package manager which you can control and view anything that a .apk package installed on your device which is developed by merging features of app_packages info, watt  & iClassyShark3xodus, into single app even though there are many package managers apps available in internet this app made by him is limitless in features with it's own material design and dark mode that makes you feel awesome. 

App manager not available on play store I don't know the exact reason but currently it was not available on play store you can download from third party sources which are trustable but keep in mind these app must require root access to perform any system level tasks. 

App manager is just limitless in features because it's is made by merging 5 to 6 apps for techy's you need to follow up thier telegram group or channel to discuss regarding latest features or bugs. 

App manager is open source you can see the code in GitHub and even contribute for the app development and it has already got many contributions by developers due to that today app manager getting updated features that are required in today's tech life, 

A open source app that was available in GitHub is more secured as the code and it's detailed documentation visible to public via GitHub so that you can see if there is anything wrong with the code, so don't worry. 

° App Info ✨

- Docs - here
- Changelog - here
- Issues - here

° App manager - download sources

• GitHub - here
• Fdroid - here
• IzzyOnDroid - here

° App manager - UI overview ✨

° App manager - package manager and viewer key features ✨

Note - These are just some of the key features recently many new features added to see check changelog. 

It is pleased to mention this feature in app manager that was recently added called UnAPKM which is a small tool that can install APKM files directly or convert them to APKS files and install them directly and if you don't know what is APKM then see APKM files are split parts of apk which introduced by google play store which is hard to install execpt for play store to install this APKM's you need a split apk installer - SAI which is a external app but with the latest update of app manager you can now easily install or convert them. 

Moreover, App manager is completely free eventhough it has potential features that no other app can provide in play store, just don't do download from unknown sources then the sources that listed by developer. 

Finally, We are fortunate to have this app manager to do a lot of apk related work in single app made by muntashir al-islam it has numerous features already and was on up-to-date everytime, do mention your user experience of app manager in our comment section below, see ya :-)