Name: Teaching Time
AU/EWE/Post DH HP
After the final battle, Harry becomes a curse-breaker for Gringotts, working mostly in Russia, Mongolia, China, and Japan with many trips to Egypt and the Great Magical Library in Alexandria. A find under the Great Wall of China sends him back in time to the 1910s. Upon explaining what happened to his future employers at Gringotts, they send him to work at sites in South America for 15 years. He returns to England to see what the goblins had found out about his trip through time. Harry had been thrown from his worksite in China to an alternate Earth who's timeline was almost exactly 100 years behind his own. Being from an alternate world, meant that he could attempt to change the timeline without the dangers of a paradox. The fact that Harry is the Master of Death and immortal means that he had plenty of time in which to do so. Harry convinced the goblins to let him work for them during the summers only, and applied for the DADA position at Hogwarts. (The Deathly Hallows of this world merged with his when he arrived.) Harry teaches Tom who becomes a very strong politician instead of a Dark Lord. Well, he's still Dark and still Lord Slytherin, but he's not an evil megalomaniac bent on world domination. They end up working together to reveal Dumbledore's growing senility and dementia.
I can see this going in many directions and having far too much fun with the many options for aliases for Harry.