Computerworld’s list includes Advanced CPU architectures, Hosted hardware, Ultra-Wideband, NAND drives, and Ruby on Rails. I don’t know if the list is in order, but Rails is listed as #1.

Equal parts design philosophy and development environment, Rails offers developers a few key code-level advantages when constructing database-backed Web applications… Released in 2004, RoR is an open-source project that originally served as the foundation of a project management tool designed by Web development company 37signals LLC. It is easily ported among Linux, Windows and Macintosh environments, and it can have a dramatic impact on the speed at which a Web development team is able to build and maintain enterprise Web sites and applications.

They also go on to list a few notable apps based on Rails and note that Rails will be shipped with OS X 10.5 Leopard.