This work presents a novel and always-available nail mounted display known as NailDisplay. The proposed display augments the use of a finger by allowing for always-available visual feedback owing to its fast accessibility and binding user controls with the display, i.e. what you control is what you see (through the display). Potential benefits of NailDisplay are demonstrated in three applications: from displaying to combining it with user controls. In the first application, NailDisplay can reveal what is occluded under a finger touch, making it a solution to operate small UI elements. In the second application, NailDisplay is complementary to an imaginary interface, helping users to learn an imaginary interface (e.g., on the users' arms) and allowing them to reassure the interface when their memory of it becomes unclear. In the third application, NailDisplay is integrated with rich finger interactions, such as swiping in the air. We also report users' feedbacks gathered from an explorative user study.