AMD/ATI has released an update of ATI Stream SDK. The ATI Stream Software Development Kit is a complete development platform to allow you to quickly and easily develop applications accelerated by ATI Stream Technology. The SDK allows you to develop your applications in a high-level language, ATI Brook+.
This new version brings the support for multiple GPUs (Radeon HD 4870 X2 and Radeon 3870 X2) in a single program.
For more information about ATI Stream, just read this whitepaper: Stream Computing Overview – PDF.