Click a peg to pick it up, then click an empty hole two spaces away to jump over the peg in between, which is removed. Jumps go up, down, left or right, never diagonally, except on the triangular board, where pegs can also jump along its slopes. Leave just one peg to win, and finish in the marked hole for a perfect game. Pick a different board from the New Game menu, and undo as often as you like (Ctrl+Z or U).
The boards
English: the standard cross-shaped board with 33 holes, starting and finishing in the centre.
French (European): 37 holes. It can't be solved with only the centre hole empty, so it starts with a different hole open.
J. C. Wiegleb: a larger 45-hole cross from Germany in 1779.
Diamond: 41 holes in a diamond shape.
Triangular: 15 holes, where pegs can also jump along the slopes.
Tips and strategy
Never leave a peg on its own. A peg with no neighbours can't jump or be jumped, so it can never be removed.
Clear the board in blocks. Empty one arm of the cross at a time rather than taking pegs from all over the board.
Keep the finish hole in mind from the start, and work back from it: your last jump has to land there.
Use undo to explore. When you get stuck, step back a few jumps and try a different line.
On the English board, the shortest solution takes 18 moves, counting a chain of jumps by one peg as a single move. Ernest Bergholt found it in 1912, and John Beasley proved in 1964 that nothing shorter exists.