The booming app market has long been a boon for homebrew developers, ripe for low-cost, high-originality thinking – but it's also encouraging a deluge of cheap marketing devices. Often, these free "spam" apps are dross dreamt up for promotional purposes and swiftly deleted from one's iDevice, but just occasionally they can offer something worthwhile.

The Ikea-sponsored Happy to Bed (free, Apple App Store) takes advantage of the modern obsession with sleeplessness to try to sell us some Swedish flat-pack furniture – but also offers a useful tool that previously would have cost 69p in the form of the Sleep Cycle app. Enter the time you need to wake up and then the number of hours of sleep you would like; placed next to the pillow the app then measures your body's natural sleeping rhythm and calculates your sleep cycle from it. Subsequently, it is able to advise the best time to go to bed. It's a nifty tool and comes with a host of handy tips for things to do to help you wind down and get a good night's rest. It's certainly not an original idea, but it saves a few pennies.

Of course, for every app doing something helpful there are a million useless ones clamouring for attention. For example, the recent Heineken Serenade app (Facebook, free) tried to tie Dutch lager to Valentine's Day by offering the chance to create a personalised song for a loved one. The "official" Spam app is surely just around the corner.