Yes, it's a bookcase. So it doesn't look that special. From the a cursory glance, it looks like the work product of an ordinary hobbyist. But redditor /u/themaestro152 of Marksville, Louisiana is a master of his craft. Watch the video and you'll see that the dividers in this bookcase slide.
The client who commissioned this custom piece wanted movable dividers, but on an all-wood project. Hidden in the undersides of the shelves are t-track slots that allow her to move the dividers where the wants to fit the organizational needs of her book collection. Careful routing, fitting, and a lot of paste wax resulted in this smooth motion.