The Android operating system is blessed with many useful applications. Some are meant to prevent friends and relatives from snooping into your smartphone or tablet, while few others can be used to boot your device faster. There are many other useful applications for various purposes which we have listed below.
Truecaller
Caller ID system helped only in identifying the numbers but the Truecaller App goes one step ahead – it shows the name and location of the number. Truecaller’s service is driven by a large and verified mobile phone community that helps in identification of the caller. It is thus a very useful application for girls (who are often harassed by anti-social elements) and for those who get irked by tele-marketeers (perhaps most of us fall into this category).
With Truecaller, a user can see the name of the caller with the number and also approximate location using 3G or WiFi connection. Apart from identification, Truecaller can also block numbers so as to avoid getting unwanted calls and SMSes.
Another interesting feature in Truecaller app is that one can perform reverse number look up for mobile and even landline numbers (you enter a phone number in the Truecaller and it will show you the owner’s name). You can also connect the Truecaller app with social networks like Facebook and Twitter, and in turn let other’s find you (you can also locate other person’s social network ID by their phone number if they have done the same). Free version of Truecaller comes with advertisements while the paid version doesn’t have advertisements.
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AppLock
Locking applications, which can reveal your private information or photos to others, is very essential and is a crucial feature that is still missing in Android. But there is an application called AppLock which allows locking applications and the gallery section which contains photos and videos. You can also choose to lock few selected photos and applications. The app also allows locking SMSes.
This application is available for free from the Google Play store.
Clean Master (Cleaner)
Majority of the Android smartphone owners find their phones going slow at times and are clueless about the reason. For them, Clean Master is the solution that removes unwanted cached files and data from the phone’s memory and SD card to make the phone more responsive and fast. Clean Master also provides memory boost by stopping all the unwanted apps in the background to free up the RAM. 
The app also offers built-in app manager to backup and uninstall unwanted apps. Clean Master comes with a neat user interface and has an easy to understand options for even a novice.
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AppMgr III
Many users keep on installing apps on their Android devices till they get a “low storage” notification that leave them clueless. This can be solved by the AppMgr III application which moves the installed apps to the SD card or internal storage from the phone storage which also makes the device a bit faster. Also, this ensures that there are no ‘low memory’ errors. 
This app has an easy-to-use user interface. The AppMgr III allows app management with a breeze in a way that the users can move a majority of the third party apps to the SD card. This app packs batch moving, batch wiping of cache-data, app list export and many such features.
AirDroid
AirDroid is a device sync application that not only allows users to transfer files from a PC to an Android phone and vice versa, but it also allows them to do a lot more on their Android devices using their computers. The application basically allows users to receive, send, forward or delete SMSes from their PCs. 
One can also install and uninstall apps in their smartphone from computer using this app. Similarly, one can control music, contacts, photos, ringtones etc of their smartphone using a computer.
AirDroid app is ideal for those who spend most of the day working on their desktops. The application allows users to connect their PCs with their Android smartphones through the internet Browser or through WiFi. AirDroid though requires connecting both Android device and the computer on the same network/WiFi. Though there are several such applications on Google Play store, the AirDroid app is the easiest to set up and use.