This is a new 4 track app called RecordStudio. Here's what the developer has to say.
A day of joy! RecordStudio for iPhone and iPod Touch (2G) is available in the app store. Record up to four tracks of CD quality audio, use the built in metronome to find the perfect groove or import your own sound files and record additional tracks on top. Download your music also on the go through the integrated web-browser.
WiFi-sync your instrumentals and recordings. RecordStudio gives you totally new perspectives in living your musical creativity everywhere you go - For only $4.99.
I haven't tried it yet, but if anyone has any experience of it then please get in touch.
App store link: