Yume Nikki (Significant)
Released in June 26, 2004 and made by Japanese developer "Kikiyama" (with updates all the way to 2007 and a Steam rerelease), this RPG Maker game is the father of horror indie games, if not the father of indie games in general. This surreal/psychological horror experience went under the radar outside of Japan for a time before an unofficial english translation was made. The game was well received by critics, with the art style, atmosphere, and gameplay being the highlights of it. The game is free to play on Steam currently, and I suggest this game if you're looking for a nice surreal experience. (please never play the 3d "remake")
OneShot is a puzzle and adventure game made by Little Cat Feet released in June 30th, 2014 as freeware and rereleased on Steam 2 years later on December 9, 2016 as an updated and extended version. The game is centered around metafictional concepts, like how the player and the protagonist, Niko, are perceived as separate characters. This games puzzles may seem simple at first, but eventually they branch out into changing different aspects of your PC (changing your background, adding text documents, etc.). The game also features a third ending where if you manually delete your save file, the game will restart but will change drastically throughout (known as a Solstice run). The games pixel art style and OST were critically acclaimed. This game is $10 on Steam and itch.io, and the freeware version is available on RPGmaker.net. Overall, a great game that I highly recommend. (assuming you know how files work lol)
Five Nights at Freddy's (Significant)
I'll be honest here. I don't really to talk about this one. Released in August 8th, 2014 and made by Scott Cawthon, this survival horror series took over the internet by storm. Originally going under the radar for a small time, the series exploded in popularity when several Youtubers made videos on the game (the most significant of which would be Markiplier). The series boasts 7 mainline games, 4 spinoffs, 9 books, and 1 upcoming movie. The first game was critically acclaimed, but every game after until the 5th would have lower and lower ratings. While not the most interesting series, it still shaped some of the internet into what it is today. If you want to experience the legacy it left for yourself, all the games are on steam.
(I'd do more games but I'm too lazy)