The Asteroids example demonstrates how Tcl code is embedded in Common Lisp.
The Common Lisp Package Viewer shows how to use the basic functionalily of clTcl.
The Fourier series example demonstrates graphics. It uses PlotChart to display harmonics of the Fourier series.
You need PlotChart. The binaries from the installation page have PlotChart already in them.
The ASDF viewer is a more elaborate example. Shows various ways to call Tcl/Tk or post events and handle errors.
Only works for SBCL and LispWorks but porting to other Lisps with multiprocessing capabilities should not be difficult.