Blizzard has announced that Overwatch will run a free trial, running November 20-26. The free trial will be for all platforms, meaning that new players will have access to the current roster of 29 heroes, including newly-released Ashe, plus 19 maps and all game modes.
Any progress you make during the free trial, such as experience gains and cosmetic unlocks, is tied to your Blizzard account and will carry over if you decide to purchase Overwatch so long as you use the same account.
The free trial period also has goodies for existing Overwatch players to earn, too. If you’ve linked your Blizzard and Twitch accounts, watching two hours of Overwatch streams during the trial period will earn you three chibi-style Ashe sprays to use in the game.