Pixel versions of printed guidebooks are handy; Lonely Planet's interactive apps can seriously enhance a trip. For Android, the travel publisher has 25 city guides that harness your phone's GPS to direct you to local attractions, from restaurants to kayak rentals; there are also 18 language helpers available (from Cantonese to Portuguese) that can "speak" a phrase aloud that you can't pronounce. For the iPhone, the offerings are deeper still: there are more than 130 apps, from audio walking tours of London neighborhoods to city guides that let you call up a gallery's website, a sushi joint's menu, or a hotel's reservations page. Tip: seek out a Wi-Fi hotspot when using the latter functions or you risk running up extravagant roaming charges. Free to $6, depending on the app; Android and iPhone.