Ambient sounds include wildlife, environmental, human and mechanical sounds. Just a few examples are birds, frogs, wind, rain, river, jungle, city, subway, the sound of typing on a keyboard, machine and fan sounds.

I use Ambiance with ear-buds to tune out background noise when coding. The rain sound effects are great at blocking out other sounds without being too distracting.

In the unlikely event of not finding a sound you like in the huge collection provided, you also have the option of selecting up to three sounds to mix together. If you want to hear frogs typing on a keyboard while being cooled by an oscillating fan, Ambiance is the app for you.

Exactly how to mix sounds is not immediately obvious when you start the app. To play several sounds at once, make sure both "Combination Mode" and "Show Front Controls" are enabled in the "Advanced" tab of the options screen.

A timer is available in the options screen, which is handy if you use any of the sound effects to help you get to sleep.

The amount of sound effects makes Ambiance a bulky application, which can cause slow syncing with iTunes. An update to Ambiance made it possible to delete sounds from the application, so you can remove sounds you don't use and cut down on the size. A fresh install of the app will return all the original sounds.

Because the iPhone currently doesn't support running apps in the background, you can't have Ambiance playing while you read your email or do anything else on the iPhone. This isn't a flaw in the application, of course, just a restriction of the platform.

Ambiance is a great app to have if you work anywhere with distractions that you'd prefer to tune out. It works wonders for my concentration when coding.

You can get Ambiance for $0.99 in the Apple App Store.

Race tracks span the Globe and are as varied as the vehicles. You can race through tracks themed on a desert, jungle, glacier, the island of Crete, the Great Wall of China, Egypt as well as Medieval and Viking towns. An underwater location themed on the city of Atlantis makes use of submarines and expands on the accelerometer-based controls to account for changing depth.

The Atlantis track seems detached from the rest of the game and feels a bit experimental, but it's a fun track to play.

Power-ups can be collected by driving into them on tracks. Power-ups enhance your vehicle with "sticky tires" or improved suspension for a limited period of time.

Weapons can be collected in the same way as power-ups and work in a similar way to Mario Cart games. You can launch bones, firecrackers, homing pigeons and oil slicks either forwards or backwards to cause trouble for the other racers.

Overall the game feels very polished. The occasional 3D dinosaur passing over a menu screen shows the attention to detail that has gone into the design. The on-screen controls fit the caveman theme, appearing as arrow heads.

In addition to well-done visuals, sound in Cro-Mag is excellent. Each track has its own music and events like collecting a power-up are accompanied by professional-sounding announcements.

There are only a couple of negative aspects of the game. Once you get the hang of the controls, the AI racers aren't much of a challenge. It's very easy on some tracks to get so far ahead that you're almost coming up behind them.

The game lacks any kind of career mode, so there are no extra tracks or vehicles to unlock as you progress. Not even your vehicle selection is remembered between racings, forcing you to choose again before playing another track. This makes Cro-Mag create for casual gaming but looses some of its appeal to players who like to work towards goals in games.

Cro-Mag Rally is $1.99 in the Apple App Store.