The App Store is a digital distribution platform, developed and maintained by Apple Inc., for mobile apps on its iOS operating system. The store allows users to browse and download apps developed with Apple's iOS software development kit. Apps can be downloaded on the iPhone smartphone, the iPod Touch handheld computer, or the iPad tablet computer, and some can be transferred to the Apple Watch smartwatch or 4th-generation or newer Apple TVs as extensions of iPhone apps. The App Store was opened on July 10, 2008, with an initial 500 applications available. As of 2017[update], the store features over 2.2 million apps. Developers have multiple options for monetizing their applications, ranging from free, free with in-app purchases, and paid. However, App Store has been criticized for a lackluster development environment, prompting the company in June 2016 to announce a "renewed focus and energy" on the store. Major changes introduced in the following months include ads in search results, a new app subscription model, and the ability for developers to respond to customer reviews. Additionally, Apple began a process to remove old apps that do not function as intended or that don't follow current app guidelines, with app research firms noticing significant numbers of app removals from the store. Furthermore, with the release of iOS 11 in September 2017, App Store received a complete design overhaul, bringing a greater focus on editorial content and daily highlights, as well as a design similar in style to several of Apple's built-in iOS apps.