Johan Rydberg has recently announced his Free Software (GPL) firmware implementation named GNUFI.
GNUFI is designed to be a firmware compatible with the Unified Extensible Firmware Interface (UEFI) specification.
GNUFI is designed so that it can be adopted to different runtime environments; such as a legacy BIOS or U-boot environment, or as a LinuxBIOS payload.
At this point there has not been any official release of GNUFI. The version controlled source repository can be accessed using Bazaar:
bzr branch http://gnufi.openbios.org/gnufi.dev
If you're interested in early testing and/or helping with development also checkout the wiki / bug tracker and the mailing list.