The sounds that can be played are things like the ocean, summer rain, heavy rain, white noise, windchimes, thunder, crickets, and various musical instruments.
There's also a random button, then lets you shake your phone and it will randomly select a few sounds to play together, or you can choose however many sounds you want to mix together yourself to play. You can also set playlists up for sounds you've combined to play.
A timer can also be set for how long you want the sounds to be played for, so you're not leaving them on all night, or you can use it as an alarm clock.
The main program is free off the Market by searching for "Relax and Sleep", and there's also an expansion you can add on, which costs £1.45, which has a link to it through the main program, which adds more playlist slots, and couple more customisation options.