The XView source code has been freely available since the early 1990s, making it the "first open-source professional-quality X Window System toolkit".[1] XView was later abandoned by Sun in favor of Motif (the basis of CDE), and more recently GTK+ (the basis of GNOME).
XView was reputedly the first system to use right-button context menus,[1] which are now ubiquitous among computer user interfaces.