In mid-June 2013, Blizzard announced testing of the Battle.net desktop app and it was released as a Beta in mid-August 2013. It appears to be a unified version of Blizzard Launcher for all of their games. It has a UI that resembles the more minimalist design of the Battle.net web site as compared with the more textured UI of the game-specific launcher. This replaces the launcher for all Blizzard games, and works similar to the current launchers, with background updates, repair tool, and more.
The Battle.net EULA (End-User License Agreement) was updated around August 1, 2013 to go with this new app.
Around version 1.1.0, the term "Beta" was removed from the app and related web pages, but Blizzard never officially announce the Beta was ending or a release.
Many options for all games, including game installation, security options, game updates, Battle.net desktop app specifics, and network details.
Installing one of the three games when they are not installed yet. The installation can be queued, meaning that if you press the INSTALL button of two games after eachother, the games will be installed in that order
The app is not dismissed when launching a game. It will continue running;
It can be minimized to Windows' System tray. It can be resized and maximized.
From "Battle.net Desktop App 1.0.6 Patch Notes" blue post
Battle.net account information should now load in much faster.
Several issues related to games not appearing properly or displaying incorrectly as "Starter Edition" should now be resolved.
Battle.net will now display an error message when launched if there is already another Battle.net client running in either another operating system or another user account.
Clicking links that log the user into their account in an external browser now have a timeout. If the request is not processed in a reasonable amount of time, the browser will open the link without the automatic login.
Qt version has been updated to 4.8.5
An option has been added to minimize the client to the system tray when launching a game (Windows).
Changes were made to how Battle.net stores your last login region and language preferences. As a result, these may change after the patch is applied.
You can change your language under Settings - General - Battle.net Language
You can change your login region from the login window
Battle.net will no longer display that a game is running if the game has not yet started.
Battle.net will no longer display that account information is loading each time the user logs in.
Battle.net will no longer report that a video card is unsupported when the video driver is updated while the Desktop App is running.
Crabby will try harder to display game content when changing game tabs.
Fixed an issue during disk installation that caused an error message to display when prompting the user to insert the next disk.
Fixed some typos in the settings menu.
Pressing the Enter key while installing a game will now default to selecting the Next button.
Fixed a graphical issue that occurred when a progress bar was paused during installation.
Many error messages were improved to be more descriptive.
Multiple other bugs were fixed.
The background images for each game have been updated