Window-based applications written with LispWorks 3 and previous used CLX, CLUE, and the LispWorks Toolkit. Such applications are restricted to running under X Windows. Because we and our customers wanted a way to write portable window code, we developed a new system for this purpose: the CAPI.
Part of this portability exercise was undertaken before the development of the CAPI, for graphics ports, the generic graphics library. This includes the portable color, font, and image systems in LispWorks. The CAPI is built on top of this technology, and has been implemented for Motif, Microsoft Windows, Cocoa and GTK+.
All Lisp-based environment and application development in LispWorks Ltd now uses the CAPI. We recommend that you use the CAPI for window-based application development in preference to the systems mentioned earlier.
CAPI User Guide (Unix version) - 30 Aug 2011