I found these Android Useful Apps Free when I needed it to perform some task on my Samsung Note Smartphone. 

SMS Backup & Restore - Ritesh Sahu
- SMS Backup & Restore is a simple Android app that backs up and restores your phone's text messages. 
Why I used it:
-- Very useful when I was helping my wife to transfer all her SMS messages her new Samsung S3.
 

WhatsApps Backup & Restore
-- You do not need any apps. Before installing whatsapps, copy your folder to your computer. 
--- Then copy the whole folder back to your new phone. 
---- Once copying done, then you install WhatsApps and all your previous phone history will be in your new phone.
 

ASTRO File Manager with Cloud - Metago 
- Organize, view, and retrieve all of your pictures, music, videos, & documents; built-in app backup & task killer; manage all your files regardless of where they are stored . 
- Steps to Backup Your Apps
-- Click Tools button
--- Click App Mgr
---- Installed Apps - Click the apps you want to Backup and Move to another Phone or Tablet
----- Click Backup
------ Once completed, plug in your usb cable and look for the Folder Backups\Apps\com.filename.apk
------- Copy the Backups files to your new Phone or Tablet
-------- Install Astro on your new Phone or Tables and copy your backups file into the Folder Backups\Apps\com.filename.apk
--------- Click Tools button
---------- Click App Mgr
----------- Click Backed Up Apps
------------ Click your com.filename.apk
------------- Click Install
Why I used it:
-- Found this when my daughter request me to help her transfer the Minecraft Apps including all her existing world from the Samsung S3 to my Note 2.
 

WinZip – Zip UnZip Tool - WinZip Computing 
- WinZip, the world's #1 zip utility, makes it easy to create, extract and share zip files on your Android device! Create and email Zip and Zipx files. 
Why I used it:
-- Bluetooth a Zip Folder with all the files to my Note2 and needed this apps to Unzip it.

Lock Screen App - Kenneth Cheng 
- 'Lock Screen App' can lock your device easily. 
Why I used it:
-- Use this to Lock my Samsung Note 2 Smartphone instead of pressing the hard button as it is faster.

Keep Screen On - Open App Info
- Prevent Browser from turning off due to phone time out. 
Why I used it:
-- There are some site where videos can only be played using the Puffin Web Browser and this app can stop the phone from auto turning off.

AppLock - DoMobile Lab
- AppLock can lock SMS, Contacts, Gmail, Facebook, Gallery, Market, Settings, Calls and any app you choose, with abundant options, protecting your privacy.
Why I used it:
-- Actually, I used this useful free apps to locked my son Samsung S2 as I got tired of telling him not to overused his Smartphone.
 

BSPlayer Free - BSPlayer media 
- For playing HD video and able to save last view video.
Why I used it:
-- There are jerking and humming sound coming from HD video when I used other video player.  Seems like BSPlayer can play HD video without those ignoring sound. 
 

AppUsage - smartappers.com
- Measures time spent on each app. See which apps to uninstall because you're not using them! 
Why I used it:
-- Basically, I used this to check how much time my son is using this phone to play games.  I locked this apps using the AppLock to prevent him from uninstall it.
 

Ringdroid - Ringdroid Team
- For cutting your favorite song.
Why I used it:
-- Trying to change the starting point of my favourite ringtone song as I could not hear it.  This apps just work great and does the task of changing your song start and end point.
 

Wakelock Detector-Save Battery - UzumApps 
- ”Wakelock Detector” helps you to detect battery consuming applications in your Android phone by checking wakelock usage history. Now you can easily find out which applications keep your phone awake and drain your battery!
Why I used it:
-- I used this apps to find those Apps that are draining my battery.  Then I use Greenify to Hibernate the batteries drain apps.
 

Nexus 10
When you create files from Android apps and plug into your Windows PC, the files are not found. 

What you need to do is to on/off your Nexus so that it re-read your folder files again.  After that, when you plug it back to your Windows PC, the files can then be found.  Hopefully, Nexus developer can fixed this bug.

Rescan SD Media Card - RADEFFFACTORY
Instead of on/off to let Windows PC read your Nexus created files, this apps can do the job by clicking it.  Pretty fast.
 

Hide Pictures on Android Gallery
Go to My Files folder, then Pictures or create a folder and name it whatever you want. Go the newly created folder, add another folder again and name it .nomedia. 

Copy or move photos in the folder (not the .nomedia coz it won't show after creating it). Then you check in the gallery, and voila! Folder isn't shown!

PS: The pictures you have copied/moved can be viewed only in My Files folder, which is much safer.
 

How To View Android Hidden Files in Windows
- First, know that the way Windows and Android differ in the way Hidden files are stored. 
-- Android Hidden Folder have the . at the Front.

In Android, set to view Hidden files by pressing the Left button at the Folder. 
- Tick Show Hidden Files

In Android, rename e.g. .temp to temp -> remove the . from the Folder

Now plug your cable to your Windows PC and you will be able to view those Android Hidden Files in Windows. 
- After copying the files, change it back with . in Android before you go back to your Android apps that is using that folder.

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