For some logic puzzles, such as Sudoku and the Picross 3D[tm] game by Nintendo, I've written automatic solving programs. This is the place where they live.
Some of you might ask "Why? Solving puzzles with a computer takes away the fun and joy of these puzzles! They're meant to be solved manually". Well, while this is true, it does not award for the actual reason one usually writes puzzle solvers:
Writing a puzzle solver actually is fun too.
At some point, just solving the puzzles becomes boring, a new challenge is needed; so I wrote the solvers. I actually have never used them (except for testing) to solve any puzzles, btw :)
Additionally, those were written on my HP 200LX, which is an early PDA, featuring DOS running on a Intel 286 CPU, clocked at 8 MHz. This made it additionally challenging, because the brute-force approach or backtracking will not work, due to time or memory constraints.
So where are they, you might ask. They're here:
A Sudoku solver, written in QuickBASIC. It's pretty slow (due to QuickBASIC being not very fast, and due to some inefficient design decisions), but has a nice user interface :). Its page lives here.
Picross 3D solver
Picross 3D is a puzzle game for the Nintendo DS. This solver is written in C and pretty fast. Have a closer look on its page.