TianoCore is an open source implementation of UEFI, the Unified Extensible Firmware Interface. UEFI (formerly EFI) is intended to replace the traditional PC BIOS. TianoCore as in implementation cannot do that, as it lacks the code to do hardware initalization. Since hardware initialization is exactly what coreboot does, the combination of coreboot + TianoCore is the most straightforward option to provide a complete, opensource UEFI environment.
There are various approaches for loading TianoCore, the easiest one is to use SeaBios floppy mechanism and DuetPkg.