Monika Before Story is a Doki Doki Literature Club mod with the premise that MC is the club president, and Monika is his childhood friend while Sayori is his classmate. The game boasts a route for each girl, new poems, some great original music, and 10-11 endings (depending on how you count them). It's definitely a mod worth playing. Some specific points I'll praise:
It keeps the spirit of the original game going as far as deleting files being part of the game and stuff. In fact, the majority of the endings are only accessible by tampering with the installation process - if you don't, you'll just get a normal VN like what DDLC itself was advertized to be. (I do recommend you do at least one playthrough without tampering before going for the true ending in order to get the full experience, even if it's not what you're here for.)
It gives you a lot of options that weren't available in the original game. When you're choosing who to spend the weekend with, Sayori and Monika are now accepted options (Natsuki and Yuri still try to guilt you out of it but since MC is the club president they fail). There's also a new option when resolving the argument on day two.
It's fun to see how the dialogue changes now that MC is the president. A lot of Monika's lines had to be transferred to him, and so Monika had to get new lines, and, instead of MC hesitating to join the club, Natsuki does.
Of course, no story is perfect, and this game like all others has its flaws.
Monika's first exclusive involves her doing something that I hope most of us would recognize as bullying in real life: She steals MC's book and runs away with it, and doesn't stop when he asks (until he gives up on catching her). The scene is portrayed like there's nothing wrong with this behavior at all. It has a very similar theme to what MC does in Natsuki's weekend scene: the idea that it's acceptable to continue messing with someone else's body or property when they explicitly tell you to stop, because "they're enjoying it" or "they're not serious". It's not quite as bad as Natsuki's weekend scene though, since it's of a much less intimate nature.
The Monika date scene was really cringey. The others were fine, but Monika's was just terrible. At least it was terrible in a funny way.
The MC hate in the "true" ending. This wouldn't be that bad in a vacuum, but the DDLC community already has a serious problem with unjustified hate toward MC (which you can see most egregiously in the popularity of MC-hating mods like A Brand New Day and Shattered Worlds). Not to mention it's a little sexist to have four girls and one boy in the story and the boy is the only evil one.