In an industry driven by the constant forward thrust of technology, labels can very quickly turn from useful signposts to restrictive dogma. Take the word "sandbox", for example. Once used to help us understand the anarchic freedom on offer in games like Grand Theft Auto, it's now become a catch-all term for games set in cities where you get to run around and blow stuff up for no reason.
As you'd expect, given its name, The Sandbox is a sandbox. A literal sandbox, mind you, into which you pour various elements and see what happens. Think of your iPhone as a cosmic petri dish, ready to see what happens when acid rain falls on a volcano during an ice age.
There are 30 elements to tinker with in The Sandbox, ranging from obvious building blocks such as dirt, sand and water, to more technological tools that enable you to construct electrical circuits, powering heaters and coolers. The sun and weather can be switched on and off, and you also have control over the climate of your tiny pocket-sized universe, freezing it solid or subjecting it to blistering temperatures. You can even unlock musical notes, transforming your improvisational landscapes into chip tunes.
Everything reacts with everything else in much the same way you'd expect in real life. Burn trees to make ash. Compress the ash under stone to make oil. Heat the oil to make fire. The water cycle, too, is fully simulated so you can evaporate, condense and freeze to your heart's content.
You're free to muck about in Free Play mode, but for those who crave structure there's always Story Mode, which serves up 24 scenarios, each with numerous challenges that must be completed. You may be asked to kickstart a dormant volcano without changing the climate. A pastoral lake requires you to create glass from the sand on its bed, freeze all the water and make it snow. You don't have to do all at once, of course, and can reset the world without losing progress, so you can concentrate on each objective in isolation.
It's more science-based than Minecraft, less concerned with placing blocks and more interested in the flow of pixels. Think of it as the quantum theory to Notch's classical Newtonian model. And, like quantum theory, it's a work in progress, with gaps and flaws held together with ideas, waiting for more elegant solutions.
Placement is fiddly, especially as the game seems better-suited to the larger screen of the iPad yet has debuted on the iPhone. You can zoom in and scroll around, but that tends to be a messy affair, leaving pixel traces wherever you touched to scroll. Some of the objectives can be a little opaque as well, with seemingly sensible solutions bearing little fruit, giving no result one time and working the next. If you really get stuck, you can unlock hints for a small amount of mana, but it's here that the dreaded in-app purchase rears its head.
Mana is used to purchase new elements to play with, and is earned by completing challenges in Story Mode, and by unlocking Achievements in Free Play. It's technically possible to complete all the Story Mode challenges and gain access to every element without paying any actual money but, as is so often the case, the game feels skewed to make that an unlikely - or at least unwieldy - proposition. Unless you're incredibly frugal, you'll eventually end up either grinding for long-term Achievements - "pour more than 100,000 pixels" - or simply biting the bullet and buying extra mana, or unlocking everything for £4.99. The balance isn't as craven as some free-to-play titles, but it is always there, nagging in the background, making you wonder if the game is going to box you into a corner you must buy your way out of.
That these commercial annoyances don't overwhelm the joys of this charming pixel art ecosystem is a testament to how much fun it can be to simply fool around with simulated chemistry and physics, and the fact that the app is free means that there's no reason not to enjoy that pleasure for as long as it lasts. Right now, The Sandbox is a slightly crude lump of carbon, but with pressure applied by a few well-considered updates, it has the potential to be a real gem.
App of the Day highlights interesting games we're playing on the Android, iPad, iPhone and Windows Phone 7 mobile platforms, including post-release updates. If you want to see a particular app featured, drop us a line or suggest it in the comments.