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 user privacy and security; part of that effort is to minimize the amount of proprietary and/or binary code. Their laptops ship with a blob-free OS and coreboot firmware with a neutralized Intel Management Engine (ME) and SeaBIOS as the payload.
All ChromeOS devices (Chromebooks, Chromeboxes, Chromebit, etc) released from 2012 onward use coreboot for their main system firmware. Additionally, starting with the 2013 Chromebook Pixel, the firmware running on the Embedded Controller (EC - a small microcontroller which provides functions like battery management, keyboard support, and sensor interfacing) is open source as well.
Libretrend sells the Librebox, a NUC-like PC which ships with coreboot firmware.
PC Engines designs and sells embedded PC hardware that ships with coreboot and support upstream maintenance for the devices through a third party, 3mdeb. They provide current and tested firmware binaries on GitHub.
Libreboot is a downstream coreboot distribution that provides ready-made firmware images for supported devices: those which 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.
MrChromebox provides upstream coreboot firmware images for the vast majority of x86-based Chromebooks and Chromeboxes, using Tianocore as the payload to provide a modern UEFI bootloader. Why replace coreboot with coreboot? Mr Chromebox's images are built using upstream coreboot (vs Google's older, static tree/branch), include many features and fixes not found in the stock firmware, and offer much broader OS compatibility (i.e., they run Windows as well as Linux). They also offer updated CPU microcode, as well as firmware updates for the device's embedded controller (EC). This firmware "takes the training wheels off" your ChromeOS device :)
Heads is an open source custom firmware and OS configuration for laptops and servers that aims to provide slightly better physical security and protection for data on the system. Unlike Tails, which aims to be a stateless OS that leaves no trace on the computer of its presence, Heads is intended for the case where you need to store data and state on the computer.
Heads is not just another Linux distribution – it combines physical hardening of specific hardware platforms and flash security features with custom coreboot firmware and a Linux boot loader in ROM.
Skulls provides firmware images for laptops like the Lenovo Thinkpad X230. It uses upstream coreboot, an easy to use payload like SeaBIOS and Intel's latest microcode update.
It simplifies installation and includes compact documentation. Skulls also enables easy switching to Heads and back.