When Dumbledore gives Harry the Resurrection Stone to help him with his Horcrux hunt (without hiding it in a snitch) the golden trio find a way to kill Voldemort without having to hunt down the Horcruxes one by one. Many lives are saved. Oneshot.
When a time-traveler accidentally ends up in the Marauders era for 60 minutes, she decides to save the life of James Potter. Single timeline.