Masyu
Also called Pearl
Draw one loop through cell centres that goes straight through white pearls and turns on black ones.
Rules
Draw one loop through the centres of cells. It doesn't have to visit every cell.
✓ One loop White pearl: go straight through it, and turn in the cell just before or after it.
✓ Turns next to it ✗ Straight on both sides Black pearl: turn on it, then go straight through the next cell on both sides.
✓ Turns, then straight ✗ Turns again too soon
Example: Pearls
Playing here: Drag from cell to cell to draw; drag back over a line to erase it.