As a result of the work of Keith Packard, David Turner, and many others, X11 now has two font systems: (1) the original Core Font System, and (2) the modern Xft system. Taken together, XRender, Xft, FreeType, and FontConfig have solved a host of problems that previously plagued the X windowing system.
Applications now have full access to font files, and thus the full control needed for advanced typography such as kerning and ligature substitution. Fontconfig provides sophisticated font pattern matching. XRender supports antialiasing on modern X servers such as X.org and XFree86, but is smart enough to fall back to the old X Core rendering when talking to X servers that do not support the Render extension.
Both Trolltech's QT toolkit and the Gimp GTK+ toolkit use Xft. As a result, the two most popular Linux desktop environments, KDE (built on top of QT) and Gnome (built using GTK+), as well as a host of other important modern applications such as the Mozilla and Firefox web browsers, all take advantage of Xft.
Developers wishing to build modern applications for the Linux operating system no longer need to be constrained by the historical X Core font system. By using a modern toolkit like QT or GTK+, or an application framework like Gnome or KDE, developers have complete access to modern font services.
While Xft along with FreeType2 and FontConfig provide ample font services, we still need to look at the question of text services, especially the problem of complex text layout (CTL) services needed for a host of important world scripts, including such scripts as Arabic, Syriac, Devanagari, Bengali, Thai, Khmer, Tibetan, and so on ...