freshly-unveiled team-based shooter, is currently playable in Anaheim for the duration of BlizzCon 2014. If you couldn't make it to this year's celebration of all things Blizzard though, there's still hope; sign-ups for the Overwatch beta are live, and all you need is an active Battle.net account.
Simply head over to the official Overwatch site and click the big yellow button that says "beta," login with your Bnet account and boom! Done.
As for when you can expect to take Blizzard's stylized sci-fi(-ish) shooter for a spin, Blizzard announced that a beta would take place in 2015, but when specifically within that year it'll happen has yet to be revealed. Still, couldn't hurt to put your name in early, right?