Read more about it here http://code.google.com/android/what-is-android.html.
I am not going to write about Android, but I'll give you a live sample.
I downloaded the Android SDK and Eclipse plug-in ( Google makes life easy :D ).
Here's the Hello World program i wrote.
By the way, T-Mobile USA will announce a mobile phone based on Google's Android OS at a New York press conference Sept. 23 (source here).
I feel it's going to be a great mobile platform , can't wait till Samsung announce their Android mobile phone :)