The Standard Library Bed has two bookcases that slide on a heavy-duty track mounted at the top of the wallbed cabinetry. Each bookcase will hold 260lbs. - including the bookcase.
Library Beds can be very simple and functional ranging from $3000 to $6000 (mostly melamine material and inexpensive woods), or they can be beautiful attractive pieces of fine furniture (of course, very functional) from $5000 to $12,000. Prices vary depending on the material, style, and layout.
You can get a Library Bed by itself to make a 2-in-1 bed, or add a home theater to it and make it a 3-in-1 Library Bed as pictured below.
Another style of Library Bed is the "Swing System." This style is typically used when adding a home theater to the unit. The Bookcases on the front of the Library Bed swing open to reveal speakers mounted on the backside, the bed face holds the TV, the deeper cabinets below slide to the sides, and then the bed can be lowered.