I'm reading The Many Lives of Cadence Lee on Royalroad and I love the premise (and the novel) but unfortunately I've already caught up. It is similar to QT but distinctly different because she doesn't replace another person already in existence and is told to "do this or you will be terminated". The MC starts over in life as a new Individual (baby, toad, and author hinted that at some point she may become an item, assuming that life would be like the book about "I Was Reincarnated into a sword" that's here on NU) in a new world every time she dies. It doesn't have to be system based, but every time the MC dies they are reborn as another life, I might check out My Disciple Died Yet Again as the synopsis hints that she keeps her memories between reincarnation. I would preference that they are reborn in a different world but it isn't a requirement.
I know of only Mystical Journey which does that. Others might have more recommendations. There is also Carefree Path of Dreams that does something similar but it is not exactly what you are looking for though.
The First Fifteen Lives of Harry August - He is reborn into himself just after he was born. He lives totally different lives nearly everytime. It's a fking fantastic novel Other than that, i unfortunately don't know of any with those requirements. The majority just stick with one reincarnation and world.