There are a number of files under the nyquist subdirectory, which
carry a non-commercial license :

lib-src/libnyquist/nyquist/xlisp/xlcont.c
lib-src/libnyquist/nyquist/xlisp/xldbug.c
lib-src/libnyquist/nyquist/xlisp/xldmem.c
lib-src/libnyquist/nyquist/xlisp/xleval.c
lib-src/libnyquist/nyquist/xlisp/xlfio.c
lib-src/libnyquist/nyquist/xlisp/xlftab.c
lib-src/libnyquist/nyquist/xlisp/xlimage.c
lib-src/libnyquist/nyquist/xlisp/xlinit.c
lib-src/libnyquist/nyquist/xlisp/xlio.c
lib-src/libnyquist/nyquist/xlisp/xlisp.c
lib-src/libnyquist/nyquist/xlisp/xlisp.h
lib-src/libnyquist/nyquist/xlisp/xlmath.c
lib-src/libnyquist/nyquist/xlisp/xlobj.c
lib-src/libnyquist/nyquist/xlisp/xlprin.c
lib-src/libnyquist/nyquist/xlisp/xlread.c
lib-src/libnyquist/nyquist/xlisp/xlstr.c
lib-src/libnyquist/nyquist/xlisp/xlsys.c

To clarify this licensing here is the response from David:

"The copyright notices in the source code are intended to suggest that 
non-commercial users need not contact me for permission. It is granted
in the source code comments. Originally, commercial users needed 
a license and in some cases paid a fee. Now, commercial use is governed 
by a BSD-like license as you've mentioned. I guess I should at least 
update my copies of the source files to say that but I have no control 
over what is floating around the net.

David Betz"