rEFInd by Roderick W. Smith is a boot manager that's made for computers based on the Extensible Firmware Interface (EFI) and Unified EFI (UEFI). A boot manager presents a menu of options when the computer first starts up. This makes it possible to have multiple operating systems on your computer and choose which one you'd like to use during bootup.
Since rEFInd is a fork of rEFIt, many features are similar. It has support for text-mode and graphical operation, auto-detection of EFI and BIOS boot loaders, user-configurable graphics and icons, the ability to set OS-specific boot options, and more. rEFInd goes beyond rEFIt and offers bug fixes, user-configurable methods of detecting boot loaders, network boot options, a configurable delay before scanning for boot loaders, ability to set the screen's graphics resolution, and much, much more.