The Lenovo N21 support is now in mainline Coreboot where as previously this Intel-powered Chromebook code was just found in the Chromium Git tree. The Lenovo N21 is powered by a Celeron N2840 dual-core CPU, 11.6-inch HD display, 2GB or 4GB memory options, 16GB SSD, and up to a 9.5 hour battery life.
With this being a modern Intel system, alas there are binary blobs to deal with for Coreboot support. Blobbed up for the N21 Chromebook are the VGA BIOS, firmware descriptor, Intel ME firmware, MRC, and external reference code binaries.
Details via this commit with the 2,000+ lines of code for adding support for this Chromebook to mainline Coreboot.
If the blobs don't scare you off and do want to play with a system having Coreboot support, the Lenovo N21 Chromebook retails for $185 USD.