Stick with us on this one -- Appcelerator has just launched an App Store, but not for apps. Instead, it's for components for apps, offering designs, templates, extensions, and other tools to app developers, who can then use those to make mobile apps for various other app stores, including Apple's own iOS marketplace. These components allow devs (for a cost or for free) to put together apps with various kinds of features together quickly and relatively easily, either leaving more time for iteration and design, or simply allowing releases to happen faster.
Most of the components on the store make use of Appcelerator's Titanium platform, which is a cross-OS setup for developing both web and native mobile apps, so any developers interested in using these components will probably need to check that out first. But once you've got that down, Appcelerator's new market is a sort of a meta-marketplace, offering pre-made services and components to devs who have more money than time to spend on development.
Essentially, this is just another indicator of how popular and gigantic the mobile app market is -- there are marketplaces for even the components that make up the apps that are selling so well.