Easy Cat Whistle is a fast and free app to generate sounds only your cat can hear. Use this to train your cat…. maybe. You can also use it as a frequency generator.
You can download it from the Android Market here.
New For 2013! There’s an HD version available here on Android Market.
You can see the HD version on GitHub here.
Update 4/2012 This is now open source and hosted on GitHub. Check it out at my GitHub page.