The creepy grey-scale side-scroller Limbo was excellent when it was released on PC in 2011, and it remains excellent today: It's moody, visually stunning, and quick to kill but not especially difficult. It's also free on the Epic Games Store for the next seven days, the latest of Epic's now weekly game giveaways.
Epic also announced that it will offer two free games next week, the wartime survival game This War of Mine and the roguelite shopkeeper sim Moonlighter. It's a two-fer because This War of Mine is rated M, which means it may be inaccessible because of Epic's parental control settings. Adding Moonlighter to the mix ensures that everyone can have a free game, and in fact Epic said that whenever puts out an M-rated freebie in the future, "we will also offer another free game that will be more accessible to players of all ages."
Back to Limbo: You've got until 8 pm PT/11 pm ET on July 25 to pick it up and I strongly recommend that you do, unless you have a serious aversion to spiders. Even if you're not especially interested in playing the whole thing, its grim, slow-paced ambiance is remarkably effective and might be enough to carry you all the way to the end.