Though still reined in from a full Marketplace release, Skype beta remains an essential addition to your Windows Phone arsenal of apps. Remember when you installed the app on your parents’ fusty old desktop back home? That’s why Skype remains relevant, even in a sea of similar video chat competitors (and copycats). Today, the app is available on most devices running Windows Phone 7.5 and above, and you can make audio and video calls over Wi-Fi or 3G. For folks ashamed of their messy hair, the app also supports instant messaging.