Anyone can download Heroes of the Storm starting today, and play it for free.
Blizzard has announced that today marks the beginning of the open beta period for Heroes of the Storm. The game is free-to-play, but you used need to either buy something or get invited by someone playing it to get access.
Not the case any more, since the beta went live in all regions earlier.
All you need to do is download the client from Battle.net.
The game loses its beta status on June 2, when it will officially launch. Blizzard promised that more heroes will be added, and that development will continue post-launch.
Blizzard also released this video to get you caught up with the new MOBA: