I don't usually rec WIPs, because I know how frustrating it is for readers when they are abandoned. But I really enjoyed reading these two WIPs, so I'll share anyway for those who don't mind the risk. The first one features a time-travelling Tom meeting Hermione pre-Hogwwarts, and then it goes into the events of book one with few deviations except adding Tom in there at times. The time in the past is as interesting as the future, with intriguing Slytherin politics that aren't too adult seeming.
It also hasn't been updated for 18 mos. although the author is still around and bookmarking on AO3. And there's almost 159,000 words of gen to enjoy.
Addendum: He Is Also a Liar by Ergott (Not Rated), Gen currently, eventual Tom Riddle/Hermione Granger
The second WIP, which is being updated regularly, is an interesting AU in which Hermione and Tom meet as children. Not time travel, just alternate reality. I like their relationship, dancing on the edge of real friendship, as much as Tom is capable of. I like this aromantic Tom--the "romance" that is developing isn't his strength any more than friendship is, so he's really stretching his interpersonal skills. In this story, there are a number of differences from canon events. 263,109 words so far, in 34 chapters.
Birds of a Feather by babylonsheep (Mature), F/M Tomione friendship to romance (if only Tom knew what romance was)