Full disclosure: this might be one of the most practically pointless smartphone apps ever. But hell it’s SO fun – and will make yo(u) smile, without fail. The lovechild of a Facebook poke and a yell hello, it sends a zingy little shout of “Yo!” to friends to whom you are connected, when you hit their names. Yo had a few teething problems with hackers, but security issues smoothed out, we’re now safe to chuckle whenever we receive a “Yo!” from friends living in tricky-to-arrange-conversation timezones (like LA), or from our loved ones when we’re stuck working late at the office – it’s a small “thinking of you” nudge when there’s not really enough to say (or can’t be bothered to say) in a text. Our tip: don’t connect to too many people (only your nearest and dearest) and be wary of the inevitable onslaught that’s sure to come any day now of companies who’ll probably want to “Yo!” you as an alert when they have news. Keep it intimate and simple. At a low level of connectivity, it’s brilliantly funny and silly. A triple “Yo!” cracks us up every time. So ridiculous, but so cool. Sure, we’ll probably tire of it, but for now it’s the hippest high-five of the digital age.