Loopy
<p>
Form a single closed loop out of the grid edges, in such a way that
every numbered square has exactly that many of its edges included in
the loop.
<p>
Click on a grid edge to mark it as part of the loop (black), and
again to return to marking it as undecided (yellow). Right-click on
a grid edge to mark it as definitely not part of the loop (faint
grey), and again to mark it as undecided again.
<p>
When you have mastered the square grid, look in the Type menu for
many other types of tiling!