The underlying concept of hypertext as a user interface paradigm originated in projects in the 1960s, from research such as the Hypertext Editing System (HES) by Andries van Dam at Brown University, IBM Generalized Markup Language, Ted Nelson's Project Xanadu, and Douglas Engelbart's oN-Line System (NLS). Both Nelson and Engelbart were in turn inspired by Vannevar Bush's microfilm-based memex, which was described in the 1945 essay "As We May Think". Other precursors were FRESS and Intermedia. Paul Otlet's project Mundaneum has also been named as an early 20th-century precursor of the Web.
