SpaceTop fuses 2D and spatial 3D interactions in a single desktop workspace. It extends the traditional desktop interface with interaction technology and visualization techniques that enable seamless transitions between 2D and 3D manipulations. SpaceTop allows users to type, click, draw in 2D, and directly manipulate interface elements that float in the 3D space above the keyboard. It makes it possible to easily switch from one modality to another, or to simultaneously use two modalities with different hands.