Android is an Open Source mobile device software suite that includes an OS (based on Linux), middleware and key apps. The Android SDK provides the tools and APIs to begin developing applications for the Android platform using Java. Android has been ported to old Pocket PC and later Palms.

Android Home & at the Wiki
Android Source
Android Developers & SDK
Android on HTC Wizard,(done it, works, but no sound/wifi yet) Nokia N810 and Palm Treo
Android Freeware apps
Official Marketplace


Features

•Rich reusable application framework
•Dalvik VM optimized for mobile devices
•Integrated browser based on the open source WebKit engine
•Optimized graphics powered by a custom 2D graphics library; 3D graphics based on OpenGL ES 1.0
•SQLite for structured data storage
•Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
•GSM Telephony (hardware dependent)
•Comms - Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
•Camera, GPS, compass, and accelerometer (hardware dependent)•Free and open source
•Rich gesture based GUI
•Rich development environment including a device emulator, debugging tools , memory and performance profiling, and a plugin for the Eclipse IDE
•Large established marketplace for apps
•Low cost for development (free OS, apps and tools) and distribution. (very modest cost to sell through the marketplace)

Having played with it on an old HTC Wizard and been impressed, I can tell you Android will be the small mobile Linux of choice for developers and phone makers. And for consumers and hackers - a nice software iphone.

There are a few problems:

1. At the moment apps only install into internal memory, not memory card.
2. The Java is a cut down Java (as it must be) but it's not one of the current cut down Javas' eg JME, so both desktop apps and JME apps will have to be changed to work. Once again 'write once, compile many....'
3. While being a Linux means there is a development skills to leverage, Android doesn't use many of the standard desktop Linux libraries, so applications will need to be rewritten.

Despite these problems and the inevitable Apple lawsuits; Android is going to be HUGE.