What companies offer downloads of free games with unlimited play?

Valve Corporation and Blizzard offer downloads of free games with unlimited play. Valve Corporation's "Team Fortress 2" requires a Steam account, and Blizzard's "Hearthstone" requires a Battle.net account.

"Team Fortress 2" is a multiplayer first-person shooter that pits two teams against each other. Players pick one of the nine classes and fight for their team's supremacy. Each class has its own strengths and weaknesses. For instance, the heavy class has higher hitpoints than any other but is also the slowest.

Blizzard's "Hearthstone" is a trading card game based on the Warcraft lore. Similarly to "Team Fortress 2," players have nine heroes to choose from. Each hero has a special ability and a unique set of cards that often complements the special ability.