Gui Models

What are the various GUI models out there?

ModelViewController
EventDriven (GUI engine mostly declarative from app developer's perspective, with optional events that can override or add behavior).
ImmediateModeGui (contrast with retained mode) is a model frequently used in games. It is also largely used in memory-constrained systems, where the memory overhead of declared object hierarchies is unacceptable (e.g., GEOS/64 allows for only 8 buttons, and text-only menus. If you wish to exceed any of these limits, you necessarily need to resort to something very close to, if not actually using, immediate-mode GUI management).