OpeniBoot is an unofficial bootloader for older Apple iThings that can run unsigned code, unlike iBoot. It is pretty buggy and the latest version is 0.3, it is made for booting Android on iThing, but it can also boot GNU/Linux along with typical iPhoneOS.
OpeniBoot prior to version 0.3 have a menu with nice bloated graphics but are less flexible. OpeniBoot 0.3 have a grub-like menu and requires menu.lst file (placed in /var/ ?).
{For some reason, OpeniBoot didn't work on iThing with iPhoneOS 4.2.1 so I "downgraded" to version 3.1.2 and it worked, though OpeniBoot console only worked on OpeniBoot 0.1 ;-; ~dolphinana}