During Blizzcon 2018, Bungie announced it's giving away Destiny 2 for free on PC between now and November 18. All you need is a Battle.net account to download the game. Once you do, it's yours to keep and play forever. Note that this is the vanilla version of Destiny 2, so it doesn't come with the numerous expansions that have arrived since the game launched last year. Even so, there's plenty to do in it. Head over gifts section and claim it
While it doesn't include Forsaken, the big Year 2 update Bungie launched in September, buying Forsaken gets you all Year 1 content as well. And if you want a taste of what comes in Forsaken, you'll be able to try out Gambit, one of Forsaken's major new modes, during a free trial that runs November 9-11. Gambit is a mode that combines PvE and PvP, so you can take down computer-controlled enemies or, at certain points, invade the opposing team's side and battle against them.