XaoS is a fractal viewer program which is designed for smooth continuous zooming. It's a great way to explore fractals such as the Mandelbrot Set. Nowadays, multi-core CPUs are the norm, but the Windows binary of XaoS does not support multi-thread operation.
XaoS is easy to build in Cygwin. The only problem is that XaoS is set up to build for MinGW (using -mno-cygwin) and Cygwin doesn't provide Pthreads support for MinGW applications. The solution is to use Pthreads-w32. Using this and running with the "-threads 4" option I'm able to use up to 100% CPU on my Q6600, and XaoS is much faster.