Develop Reference

How to Group Applications at Build Time

Being a bit new to android and compiling my own images for my device, I was trying to figure out how to do the below in the source code directly.
How can one group applications in folders on the home screen at build time when building/compiling the device image?
Follow-on question to this, how can one configure the apps that appear in the home screen bottom row?
Thanks

This is not really done at build time, but you need to update the launcher xml configuration panels to state which apps you want and in there you can also create a subfolder to regroup applications.

Change layout of the built-in application

Is it possible to change the layout of the built-in application of the Android?
I have Samsung S Duos and I want to change layout of some application(dialer, SMS messenger and phone book(contacts) are not so user-friendly for dual SIM cards)
Is it possible to make buttons of this applications bigger or smaller or to add a new option (sub menu)?
If yes, is there easier way than rewriting and compiling whole Android source? Or maybe there is an option to change the phone book(contacts) and reinstall it as a new application?
Any help is appreciated

Is it possible to make buttons of this applications bigger or smaller or to add a new option (sub menu)?
Somebody with sufficient experience could do this, yes.
is there easier way than rewriting and compiling whole Android source?
No. And even that is insufficient, as the result will not run on your phone without the requisite drivers.
Instead, find a ROM mod that can run on your phone, then start with that ROM mod's source and make your changes.
Or maybe there is an option to change the phone book(contacts) and reinstall it as a new application?
It is conceivable, though unlikely, that the maintainers of your chosen ROM mod have arranged for some of these apps to be buildable as SDK apps. Most likely, this is not an option for you.

I guess you can't just edit the application without having the source and recompiling it. You can modify your build.prop to edit your screen density value. If you change this, you will have more (Or less) buttons etc. on your screen. But editing this file is very dangerous and I don't recommend it.

Ok first off your the one that needs help so you dont have to be rude, secondly the source code is not going to be in your phone because its going to be a binary file. And unless you know how to convert a binary conputer kanguage fike to source code then your sol. This website is not a place where we write code for you. If you have no code to display then theres not much we can help with. And the only people that have the actual source code are going to be the developers that made the application which are the developers that made your phone. In this case shoot an email to your phones company which is samsung and see if they will release you an open source code that you can go off of. That should answer your question on how to get the source code. If they dont give it to you then you cant get it.

Multi Window App Development

I want to develop an android application which has to run two other applications on the device with one app on upper half of the screen and the other in lower half of the screen. Any clues/suggestions to start developing this ? Thanks in advance !

it's not possible multi-pane-layout two other apps.
if u want your app with multiple activities follow this tutorials for your references:
it's called named as multi-pane-layouts and offical introduction about multi-pane-layouts below link:
http://developer.android.com/design/patterns/multi-pane-layouts.html
and it's shows how to implement multi-pane-layouts on your project below link from android official side:
http://developer.android.com/guide/practices/tablets-and-handsets.html
and you can download example project from github below link:
https://github.com/faisalgeek/MultiPaneAndroidApp

This is not possible, except via custom device firmware or ROM mods. In standard Android, only one app can be used at a time.
However:
You are welcome to support multi-window apps on some Samsung devices, as they have extended their firmware to support this concept
You are welcome to have an activity's theme set up to not fill the screen, though anything else around the activity will at most be visible and will not respond to touch events
If all of these applications are yours, combine them into one app, and then you can display elements of that app alongside other elements of that app however you wish.

If you are looking for a feature for your app which supports multi-window then Latest Android version N has a new cool feature called Multi-window support, you can let your app support multi-window which can be resized and scaled which is exactly your requirement. you can find the reference link here

Android Development

Is it possible for a program to mimic the Android Homepage? Can widgets, contacts, and canvases all interact at the appropriate FPS? Is it possible for an app to make calls and IMs? Or are the ISOs used to make the original too different from Java to mimic correctly?

To a large extent yes . For a start have a look at the home app sample provided by google . http://developer.android.com/resources/samples/Home/index.html .
Once you get your home app working perfectly you can add modules which practically do everything , but a better design strategy is to split the modules which do different work , so you calling module can be a different app.
I dont think there should be a fps issue if you have good code :) .

split the screen into two parts

I need to split the Android screen into two parts and run 2
applications (app A and app B) simultaneously.
App A will run on screen 1 and App B will run on screen 2. Both are visible to the
users. I need to implement this thing in the Android Framework.
I do not know much about the android framework and this is urgent and should be done on android 2.1
Is this possible, if yes please explain the procedure to achieve this.
Thanks in advance.

Implement Application A as a ActivityGroup and run Applicatoin B inside of it.