Hacker winocm has released a set of tools to help users dual-boot another operating system on their iOS device. He recently demonstrated the triple-boot of iOS 5.1, iOS 6.1.3, and iOS 7.0.6 on his iPad.
The hacker notes that "This is one of the last public projects I will push for now. Personal reasons, mainly stress related." Hopefully, we'll still see the release of the untethered iOS 7.1 jailbreak he demonstrated earlier this month.
Winocm