Simulated annealing is a powerful technique for coming up with approximate solutions to hard combinatorial optimization problems.
Several Tcl'ers have expressed interest in writing something about the topic, and this page is here in hopes of prompting more interest.
One application of simulated annealing is Solving cryptograms. The code on that page has a fairly generic implementation of the basics that could be lifted out and applied elsewhere. In fact it was lifted out of another application that did screen layouts of Message Sequence Charts, and had the screen layout problem replaced with the codebreaking problem.
Other applications are placement-and-route of transistors on a chip, chips on a pcb, logical cells in an FPGA, all kinds of scheduling problems, ...