LispWorks uses GTK+ as the default window system for CAPI and the LispWorks IDE on Linux, FreeBSD, AIX and x86/x64 Solaris. GTK+ is also supported on Mac OS X as an alternative to Cocoa. LispWorks requires GTK+ 2 (version 2.4 or higher).
Note: LispWorks on SPARC Solaris does not support GTK+.
A few known problems are documented on Problems with CAPI on GTK+.
LispWorks Release Notes and Installation Guide - 2 Mar 2015