The App Center Facebook announced last month is open for business. The phased rollout will ultimately give all its US users access to 600 apps, like Pinterest and Draw Something, reports TechCrunch. Unlike Apple's App Store and Google Play, though, Facebook's App Center is more of a discovery hub, taking users to Apple or Google or elsewhere to download the apps. And, of course, Facebook's App Center puts the emphasis on sharing, recommending apps based on what your friends are using. Some early reaction: