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