Desktop cube
Virtual desktops mapped onto the faces of a cube you spin with the mouse — Compiz's signature act, and the window system's answer to a concept car.
The idea predates the graphics cards that could carry it: Brad Wasson's 3D-Desktop from 2002 showed X desktops as a rotating carousel in OpenGL, and Mac OS X Panther switched users in 2003 by turning the whole screen like the face of a cube. But it was Compiz in 2006 that made the cube a household word. The cube plugin put each virtual desktop on its own face, with a sky behind it and the windows stuck to the surface, and rotate let Ctrl+Alt+drag spin the lot. With two desktops you got a slab, with more a prism. Beryl and Compiz Fusion added transparency, reflections, a cylinder and a sphere variant, and, as a nod to glxgears, gears turning inside the hollow cube.
The usefulness was debated even then: a pager shows the same information without the screen turning away from you. But the cube was what got Linux installed at trade shows, and it proved that once windows were textures, the compositor could do anything with them. KWin got its cube in 2008, dropped it when the code had rusted, and rewrote it for Plasma 6 in 2024, which says something about demand.