The new Battle.net Client has been in beta for quite some time now, but you had to be invited by Blizzard. But now, the Battle.net beta client is available for all to download if you want to check it out. Essentially Blizzard’s take to Steam and Origin, the client is a standalone launcher for you to easily access your Blizzard Entertainment games. The launcher will automatically download and update your installed games while keeping you up to date with Blizzard news. According to the company, the game launchers for current existing titles (StarCraft II, Diablo III, and World of Warcraft) will be automatically updated to the new desktop app once it leaves beta.
The launcher offers a new, single sign-on functionality to allow players to log in once in order to access all their Blizzard Entertainment games. It will stay logged in for up to 30 days and players can install games directly through the app. If they choose to leave the app running on their desktop, the games will automatically be updated even when they’re away from the computer. Of course, you can exit the app at any time.
This is essentially an open beta testing process for the desktop client and once the open beta ends, everyone’s launcher will be updated automatically when they start up the individual launcher for a Blizzard game.
Source: Blizzard