KnightL is an app that calculates the shortest path for a knight to get from one square to another on a chessboard. More detailed information and instructions can be found on the "Releases" page, but this document shows some pictures of the app.
The knight will find a shortest path to any tile you click on and number the steps to get there. The knight starts in the top-left corner, but you can move him my middle-clicking a new start tile.
You can disable tiles by right-clicking on them. When trying to find a path, the knight will not use disabled tiles.
You can change the movement rules of the knight as well as the size of the board. Instead of moving 2 steps in one direction and 1 in the other, this knight moves 4 steps in one direction and 1 in the other.
The instructions from the "Releases" tab also appear in the app.