Blizzard's success with World of Warcraft is mainly due to the possibilities that it offers us to expand the game by means of incorporating add-ons and including more missions, characters, and other elements for our games. The latter can be found on different webs but there's a much more efficient and faster way of finding them: WowMatrix.
Download applications and extensions for World of Warcraft
It's quite obvious that you're going to need World of Warcraft to be able to use this tool. In fact, you need to install in exactly the same location as the EXE file. Once installed, when you run the program it will show you all the extensions available for the game as well as those that you've already installed and are using.
It also comes along with a function that allows us to manually search for new add-ons. By simply double-clicking on any of them, this extension manager for World of Warcraft will start the installation automatically.