Cedar (Xerox PARC)
Xerox PARC's programming environment of the early 1980s, in which the whole screen was a set of tiled windows in two columns — the origin of the strictly tiled tradition that runs through Oberon to today's tiling window managers.
Cedar grew out of PARC's Computer Science Laboratory from 1979 as the successor to Mesa, as both a language and an environment. The language gained garbage collection and types that could be resolved at run time, and around it an entire system was built for the Dorado workstation: the Tioga editor, used for code and documents alike, a compiler that ran incrementally, and the Viewers window package. Viewers split the screen into two columns in which every window took the full column width and stacked vertically without overlapping; closed windows sat as small icons along the bottom edge. Warren Teitelman's 1984 paper "A Tour Through Cedar" described the environment to the outside world.
The Alto world had invented overlapping windows in Smalltalk, so the tiling was a deliberate choice: every pixel should be legible and nobody should have to hunt for something hiding behind something else. The idea travelled on with Niklaus Wirth, who spent his 1984–85 sabbatical at PARC and carried the image of Cedar home to ETH Zürich, where the Oberon system was built with the same two-column tiled screen. Rob Pike's Acme for Plan 9 in turn names Oberon as its model. A little of Cedar lives on every time someone opens a terminal in dwm.