See also top-level FAQ page
and Unix FAQ page.
List of questions in this category
For desktop compilation, you only need X11 (not Xt, GTK+ or any other widget set).
For embedded use, Tiny-X should work fine too.
There is incomplete support for Microwindows (the Nano-X API).
The following classes and features are not yet implemented: wxSpinCtrl, wxSocket, wxToggleButton, clipboard classes,
drag and drop classes, tooltips.