Our Final Heartbeat is a Doki Doki Literature Club mod with the premise that Monika wants to go back and undo the damage she's done to the other girls, but needs your help to do it.
The mod is nothing terribly impressive; but it doesn't have any serious flaws either. I would recommend it, especially if you just want to see a wholesome, happy ending to the Dokis' story.
My biggest criticism (in fact, my only criticism) is that after the Sayori part you're given the impression that you have to do something to save each of the girls, but in the Yuri part, your opportunity to act doesn't come until way later than I expected, so I thought I had failed by not going into the game files and doing something, but it turned out I was on the right path after all. In the Natsuki section, you don't even make a choice. Monika just saves the day all for you.
Game file secrets: there are two new character files, mc.chr (which is a PNG of a flower in greyscale) and monik.chr (only visible under /game/characters), which is the binary-encoded ASCII text "I'm still here for you. Let's save them, okay?".