Want to book a luxury suite in Luxembourg, or find a restroom in Rome? There’s an app for that, and then some. An estimated 17,000 travel apps are now available. We’ve tried a lot of them, and even produced two ourselves. Here’s a look at some of the most useful, straightforward, do-what-they-promise travel apps. They have gotten us out of travel jams, acted as cyber-concierges, and hooked us up with what we needed in a flash.