Closet doors are available in several styles and configurations.  Some of the more common types are shown below.  With available hardware, virtually any interior door can become a closet door.  Closet doors, like most interior doors, are typically 1-3/8 thick.  Browse through all  interior door styles to see the many possibilities.  Louver closet doors are also available as boxed sets.
Mirrored Wardrobe By-Pass
Mirrored Out-Swing
Moulded Hardboard By-Pass
Louvered By-Pass