WhatsApp If you know what's up, you use WhatsApp. The app is consistently one of the top downloads in the iTunes store. It may cost 99 cents, but it essentially enables text messaging for free. WhatsApp also makes group messaging easy. WhatsApp lets you put a status update, such as "at the movies," or "battery about to die." That way your contacts know why you're not getting back to them. WhatsApp also enables read receipts, so there's no need to confirm that your message was seen. Even before you send your message, it will tell you if your contact is active. The messaging app makes it easy to incorporate video and other images (such as maps) into messages. It also lets you send voice messages to your friends throughout the globe. The service is especially popular in countries with expensive SMS (standard messaging services) rates. And with over 200 million active users, WhatsApp is bigger than Twitter. WhatsApp is so popular, that it keeps fighting billion-dollar acquisition rumors. No, they are not in talks with Google or Facebook, but that doesn't mean they won't be, some day! The app is compatible with iPhone, iPod touch, and iPad, but requires iOS 4.3 or later. It is also available for Android.