Access to Hardware including Camera, GPS, and Accelerometer :

Android includes API libraries to simplify development involving the device hardware. These ensure that you don’t need to create specifi c implementations of your software for different devices, so you can create Android applications that work as expected on any device that supports the Android software stack.

The Android SDK includes APIs for location-based hardware (such as GPS), camera, network connec-tions, Wi-Fi, Bluetooth, accelerometers, touch screen, and power management.

Native Android Applications :

Android phones will normally come with a suite of preinstalled applications including, but not limited to:

• An e-mail client compatible with Gmail but not limited to it.
• An SMS management application.
  
• A full PIM (personal information management) suite including a calendar and contacts list, both tightly integrated with Google’s online services.
• A fully featured mobile Google Maps application including StreetView, business finder, driving directions, satellite view, and traffi conditions.
  
• A WebKit-based web browser.
  
• An Instant Messaging Client.
  
• A music player and picture viewer.
  
• The Android Marketplace client for downloading thied-party Android applications.
  
• The Amazon MP3 store client for purchasing DRM free music.

All the native applications are written in Java using the Android SDK and are run on Dalvik.

The data stored and used by the native applications — like contact details — are also available to third-party applications. Similarly, your applications can handle events such as an incoming call or a new SMS message.

The exact makeup of the applications available on new Android phones is likely to vary based on the hardware manufacturer and/or the phone carrier or distributor. 

More XML Layouts :

RelativeLayout :

Each child element is laid out in relation to other child elements. 
Relationships can be established so that children will start themselves where a previous child ends. Children can relate only to elements that are listed before them. So, build your dependency from the beginning of the XML file to the end.

AbsoluteLayout :

Each child must be given a specific location within the bounds of the parent layout object. The AbsoluteLayout object is probably the easiest to build and visualize but the hardest to migrate to a new device or screen size. 

TableLayout :

TableLayout is a layout object that allows you to specify table rows. 
Android tries to arrange each of the child elements into the correct row and columns.