Some mobile games are just going to go viral and today's App of the Day is typical of those games that are eminently playable.It fuses together an incredibly simple game concept, that's easy for anyone to play, as well as a social element when you can't ask the person next to you on the sofa.4 Pics 1 Word\nFormat\nAndroid\/iPhone\nPrice\nFree\nWhere\nGoogle Play\/iTunes\nThe precisely named 4 Pics 1 Word doesn't really need much of a description. The app gives you four pictures, from which you have to deduce the one word that they all point to.That might be a theme across the images, it might a colour or an action. Sometimes the answer is very obvious, sometimes it'll have you pulling your hair out.To help you along the way, there are a couple of options for getting hints. First, you can seek help from Facebook, putting the tricky level out there for your friends to help you with.\u00a0If that's a bit too embarrassing, because some of them are very obvious, then there is a coins system to help too.As you play you are rewarded coins for getting the correct word. These can be traded for hints as you play, by tapping the relevant buttons.\u00a0There are two options here. The first, which costs you 60 coins, will give you one correct letter in the word you're trying to guess. The second, which costs 90 coins, will delete some of the letters that are incorrect.These options will help you narrow down what the right answer might be, but they are rather expensive, as coins are earned only slowly. And yes, there's an in-app option to buy more coins, which is where the developers are hoping to make money from you.The app is free (hence the in-app purchase) and occasionally you'll get an irritating pop-up suggesting you install another app from the developers. We've resisted so far, just to be awkward.There's not doubt that 4 Pics 1 Word is already something of a classic. It's not too taxing, it's fun for all the family and it\u2019s perfectly sociable. We love it.