Untangle
Drag the points until no two lines cross
Drag a point to move it; letting go off the board cancels. Or select a point, press Enter to pick it up, move it with the arrow keys and press Enter to put it down (Escape cancels). Arrow keys jump between points; Space and Shift+Space cycle through them. Ctrl or ⌘ Z undoes; Shift Z redoes.
Progress saves on this device.
How to play
Some points are joined by straight lines, and some of those lines cross. Move the points until no line crosses another. Lines may meet only at the points they share: a point resting on another line counts as a crossing.
Every puzzle can be untangled. Show crossings marks the lines that cross, in a dashed red. Snap to grid drops points on a grid fine enough to untangle any of these puzzles. Numbers labels the points so you can tell them apart.
Once you untangle the puzzle it counts as solved, even if you tangle it again. Solve moves every point to the answer and does not count as a win. Restart puts the points back on the circle and clears your moves and their history.
Based on John Tantalo’s Planarity. Engine: Simon Tatham’s Untangle. MIT license and credits.