I can't keep track of the number of times I've heard a new notebook touted as a "MacBook Air killer." Apple's incredibly thin notebook hit the scene in 2008 and one of the first to do away with the optical drive and ship with speedy flash-based storage.

Manufacturers from all walks of life have been trying to emulate it ever since, directly resulting in the creation of the Ultrabook classification.

HP's new Spectre x360, first shown off at this year's Mobile World Congress, may be one of the best efforts yet from the PC industry (also check out the gorgeous new Dell XPS 13). 

Described as its most premium and versatile PC it has ever produced, HP's latest is built within a unibody aluminum chassis that measures just 15.9mm thick and weighs 3.3 pounds. It includes a 13.3-inch convertible display operating at a resolution of 1,920 x 1,080 (a Quad HD version is in the works) and is powered by up to an Intel Core i7-5500U CPU, Intel HD Graphics 5500 and 8GB of DDR3 RAM. There's also the option for up to 512GB of solid state drive storage.

Other specifications include a 3-cell 56WHr lithium-ion battery that should be good for up to 10 hours of use, a backlit keyboard and dual-band 802.11ac Wi-Fi from Intel. It runs Windows 8.1 out of the box.

Pricing starts at just $899.99 if you're alright with a Core i5 processor, 4GB of RAM and 128GB of storage. The upcoming high-end model with Quad HD display, Core i7 chip, 8GB of memory and 512GB of storage will set you back $1,399.99. All models (minus Quad HD) are shipping as of today.