Around a year ago, I started working on emulating an iPod Touch 1G using the QEMU emulation software. After months of reverse engineering, figuring out the specifications of various hardware components, and countless debugging runs with GDB, I now have a functional emulation of an iPod Touch that includes display rendering and multitouch support. The emulated device runs the first firmware ever released by Apple for the iPod Touch: iPhoneOS 1.0, build 3A101a. The emulator runs iBoot (the bootloader), the XNU kernel and then executes Springboard.
This is quite impressive.