It's difficult to build applications with a graphical user interface that uses a low-level library such as Xlib. The Xt Intrinsics library (or simply Xt) simplifies this task by providing a library of C language routines designed to facilitate the interface to Xlib. Xt is a standard established by the X Consortium that provides an object-oriented programming style in the C language. Xt routines can be used to create interface components called widgets. OSF/Motif, for example, uses Xt to create its widget set (see "OSF/Motif and IRIS IM").
Silicon Graphics implements Xlib and Xt as defined by the standard and supports them as dynamic shared libraries.