The MacBook 2,1 model that was the second-generation Apple laptop from late 2006 to mid 2007 now can be handled by Coreboot as an alternative to the proprietary Apple UEFI. Unfortunately, the newer Apple MacBook / MacBook Pro models aren't supported by Coreboot at this time.
Even with the 2006/2007 MacBook and Coreboot, the initial support lacks EC and audio support. But then fortunately there was an EC handling ACPI implementation for the battery indicator and lid status. More of the MacBook functionality will likely be implemented in due time under Coreboot.
Details on the various systems supported by Coreboot and their state can be found via the Coreboot Wiki. In terms of modern hardware support, the best mobile platforms supported by Coreboot tend to be the Google Chromebooks.