This is a thinner (almost 1in thick) version of the full size double Horizontal Top-Bar Hive. 
Its internal dimensions are standardized, and it comes with rough-sewn interior, 10 bars and a front end shim (place by the end peace near the entrance to provide bee space before adding all the bars), and a marine plywood lid. Unpainted
It is Amish hand-crafted right here in the heart of the USA. 
 
Why is it called a FLEX NUC? 
It is part of the Bee Mindful Horizontal Hive system, and is a great, flexible, multi-purpose tool to keep on hand, either in complement to a full size Horizontal Top-Bar Hive apiary, or as a stand-alone for a medium size colony (up to 10 combs) or to dip your toes into Horizontal Top-Bar beekeeping before going full size.
Here are the various purposes it can be used for:
make a FLEX hive by connecting it to a 5Frame, 8Frame, 10Frame Langstroth deep.
start a package
catch a swarm 
use as a swarm trap
house a cutout
house a split
use as a place holder for the comb with the queen on it
harvest honey comb
transport or temporarily store emty comb
queen rearing
raising NUCs
transporting coolonies between locations