coreboot doesn't provide binaries but provides a toolbox that others can use to build boot firmware for all kinds of purposes. These third-parties can be broadly separated in two groups: Those shipping coreboot on their hardware, and those providing after-market firmware to extend the usefulness of devices.
Purism sells laptops with a focus on privacy and part of that is their push to remove as much unaccounted code (that is, binary only) from their devices as possible.
All Chromebooks (and related devices) that hit the market after 2013 are using coreboot as their main firmware. And even the Embedded Controller, a small microcontroller to support various peripherals (like battery management or the keyboard) is running open source firmware.
Libreboot is a project that provides ready-made binaries for platforms where those can be built entirely from source code. Their copy of the coreboot repository is therefore stripped of all devices that require binary components to boot.
Matt Devo provides replacement firmware for various Chromebooks. Why replace coreboot with coreboot? You might want to do different things than what the Google engineers prepared for the mass market, that's why. This firmware is "with training wheels off".
John Lewis also provides replacements for Chromebook firmware, for the same reasons as Mr. Chromebox. It's a somewhat different set of devices, and with different configurations, so check out both if Chromebooks are what you're dealing with.