Instantly Reboot into a different Operating System, with iReboot
iReboot is a free program that sits in the taskbar and lets you choose which operating system you want to reboot into.
Instead of pressing restart, waiting for Windows to shut down, waiting for your BIOS to post, then selecting the operating system you want to boot into (within the bootloader time-limit!)
You just select that entry from iReboot and let it do the rest!
