The Android team have released NDK 1.6 rel 1. This is the Native Development Toolkit toolkit which allows developers to code Android apps using native Linux code, with a few limitations. The point of this is raw speed and efficiency - software using this system bypasses the java layer to hit the metal directly. As this code is written for Linux the language used is usually C or C++. The new release adds support for OpenGL ES 1.1 (Open Graphics Library for Embedded Systems), which is focussed on 3D graphic support. The build system has also been simplified and all NDK 1.5 users are encouraged to upgrade.

The NDK supports Windows XP, Mac OSX and Linux. The native libraries can only be used on devices running the Android 1.5 platform version or later. This is due to toolchain and ABI related changes that make the native libraries incompatible with 1.0 and 1.1 system images.

Using native code from java may seem daunting to new users, so the system ships with several example projects ranging from a first steps "hello world"  project to a 3D OpenGL ES example.

Source: Android developers