GNU AWK original documentation: ftp://ftp.gnu.org/pub/gnu/
The Cygwin Toolset, the UNIX environment on top of Windows 95: http://sourceware.cygnus.com/cygwin/
Programming with POSIX Threads by David Butenhof: http://cseng.aw.com/bookdetail.qry?ISBN=0-201-63392-2&ptype=1482
POSIX Threads for Win32: http://sourceware.cygnus.com/pthreads-win32/
The retargetable C compiler LCC: http://www.cs.princeton.edu/software/lcc/. Jacob Navia has ported LCC to Win32 and has included the Win32 API documentation into his distribution at http://www.cs.virginia.edu/~lcc-win32/.
A recipe for building a cross compiler: http://www.cygnus.com/ml/gnu-win32/1999-Jan/0572.html. This allows you to work with Linux and the GNU Tools to produce programs which run on Win32.
Peter Hawkins took the DirectX and multimedia files from the LCC compiler and integrated it into the Cygwin Toolset at http://www.ozemail.com.au/~peterhawkins/directx.html.
The ultimate source of Win32 API information: http://msdn.microsoft.com/library/default.htm
The Single UNIX specification (XPG4): http://www.rdg.opengroup.org/unix/online.html. The printed book, ISBN 0-13-575689-8 (CD-ROM included with the full set of documentation): http://www.UNIX-systems.org/version2/
Linux OSS, the open sound system: http://www.opensound.com/
Alan Cox has some useful information on Linux SMP at http://www.uk.linux.org/SMP/title.html and on free sound drivers at http://www.uk.linux.org/OSS/.
The Advance Linux Sound Architecture (ALSA) is compatible with OSS and looks superior when several PCI sound cards are needed: http://www.alsa-project.org/
The Duffing oscillator is derived and analyzed with many elucidating pictures in chapters 1 and 6 of Thompson & Stewart's book Nonlinear Dynamics and Chaos—Geometrical Methods for Engineers and Scientists, Wiley and Sons, http://catalog.wiley.com/title.cgi?isbn=0471909602
Finite Differencing is explained in chapter 5.4 of Brook & Wynne's book Signal Processing—Principles and Applications, Edward Arnold, ISBN 0-7131-3564-6.
Georg Duffing's original book appeared in 1918 as Erzwungene Schwingungen bei veraenderlicher Eigenfrequenz, Vieweg, Braunschweig.
The Art of Doing Science and Engineering, Richard W. Hamming, ISBN 90-5699-501-4, page 35.
The Unix Programming Environment, Kernighan & Pike, Prentice Hall, http://netlib.bell-labs.com/cm/cs/upe/index.html
Introduction to Multi-Threaded Programming, Brian Masney, Linux Journal, May 1999.
All listings referred to in this article are available by anonymous download in the file ftp://ftp.ssc.com/pub/lj/listings/issue66/3577.tgz.