https://www.gamespot.com/articles/get-overwatch-and-more-pc-games-for-12-in-septembe/1100-6461636/

October's Humble Monthly is available, and it's a doozy. If you subscribe between now and October 5, you'll get immediate access to Overwatch, Blizzard's enormously popular hero shooter that normally retails for $40. A one-month subscription only costs $12, and Overwatch is yours to keep and play forever, even if you unsubscribe. On October 5, a number of other games will be revealed that you'll also get to keep. This is an incredible deal for anyone who plays on PC and hasn't picked up Overwatch yet.

If you keep your Humble Monthly subscription going, you'll also get free Overwatch loot boxes in November and December, in addition to those months' free games. Loot boxes contain cosmetic items like skins, emotes, and voice lines for the heroes.