iPhone hacker Niacin has just released his version of iBooter.
Running on Mac, Windows and Linux, iBooter offers an interactive diagnostic and customization tool that talks directly with Apple’s iPhone bootloader.
With it you can set environmental variables, write a custom picture to the display (faboo if you’re tired of that USB plug and the iTunes logo), run USB commands and diagnose why, for example, your iPhone isn’t booting correctly.

» iBooter offers iPhone diagnostics