The second beta is available on Apple’s developer site and it features Interface Builder, Xcode IDE, Instruments, iPhone simulator, frameworks and samples, compilers, and Shark analysis tool.

In a short notice on the website, Apple explained that Interface Builder is an application for designing and testing user interfaces.

“Developers can use Interface Builder to create user interfaces that follow the Mac OS X human-interface guidelines by dragging user-interface elements from a palette of predefined controls and dropping them into the window or view they are configuring," Apple said.

The iPhone SDK was unveiled by Steve Jobs on March 6, during an event held at the company’s headquarters.

During his speech Steve Jobs announced also the AppStore, which is included in the iPhone 2.0 software. It is a new application that lets users browse, search, purchase and wirelessly download third party applications directly onto their iPhone or iPod touch.

Practically, every developer can submit their applications to the AppStore; Apple would retain 30 percent of all sales revenues.

Shortly after the launch, Apple announced that the iPhone SDK has been downloaded ober 100,000 times.

The final version of iPhone SDK is scheduled to be released in June, most probably at Apple’s WWDC.