Metaio released their Unifeye Mobile Augmented Reality SDK at Mobile World Congress 2010.
The Unifeye® Mobile SDK is the world´s first and only software development kit for creating mobile augmented reality (AR) applications. The professional toolbox is supporting all major mobile platforms and features the latest image recognition technologies, 3D rendering for animations with real time interaction and optimized components for mobile hardware. With the Unifeye® Mobile SDK software it is possible to create fascinating marketing experiences, intuitive information design, mobile augmented reality games or innovative retail solutions. Based on the proven AR platform Unifeye® by metaio it is possible to easily develop and deploy solutions at the interface between the real and virtual world.
Having used their beta Unifeye software last year, I can attest to the ease of use. However, I have not used their mobile software development version so there may be some differences.