Android

The Android platform is a software stack for mobile devices including an operating system, middleware and key applications. Developers can create applications for the platform using the Android SDK. Applications are written using the Java programming language and run on Dalvik, a custom virtual machine designed for embedded use which runs on top of a Linux kernel.

android documentation

The core Android APIs will be available on every Android phone, but there are a few APIs which have special concerns: the "optional" APIs.

These APIs are "optional" for two reasons. First, they're optional in the sense that you don't need to use them. For example, you can't write an application without using the Activity and Intent APIs, but your application may not need to know where the user is, and so you may not need the Location-Based Services API. In this sense, the LBS API is optional where the Activity API is not.

1. Location-Based Services
2. Media APIs
3. 3D Graphics with OpenGL
4. Low-Level Hardware Access

Google APIs and Services in Android

1. MapView
2. P2P Services Using XMPP