Apple have announced a new scheme for their developers, the Mac Developer Program, based on the same system as the iPhone Developer Program and eventually replacing the current ADC scheme. Priced at $99 per year, the Mac Developer Program gives access to early builds of OS X, developer boards and technical support, and various tools to produce software for the platform.
"Modeled after the highly successful iPhone Developer Program, we've relaunched the Mac Developer Program to offer members technical resources, support, access to pre-release software, developer forums and more, all for just $99 per year. As our developer base continues to grow in leaps and bounds, we're working hard to ensure we provide our developers with everything they need to create innovative applications for both the iPhone OS and Mac OS X." Apple
One of the most notable differences between the Mac Developer Program and the previous ADC scheme is that Apple have seemingly removed the Hardware Purchase Program. That gave developers a discount on buying new Mac hardware.
If you're currently mid-way through your ADC membership then that won't automatically expire - instead you can complete the term and then sign up to the new Mac Developer Program instead. More details of the scheme in Apple's FAQ here.