What Is It?
Network Manager is a sophisticated automatic network connection applet/daemon. It offers support for wired as well as wireless network connections.
From the project's website:
Networking on Linux should not suck like it does right now for the desktop user. The desktop user should never need to use the command-line to configure their network; it should "Just Work" as automatically as possible and intrude as little as possible into the users workflow. The computer should use the wired network connection when its plugged in, but automatically switch to a wireless connection when the user unplugs it and walks away from the desk. Likewise, when the user plugs the computer back in, the computer should switch back to the wired connection. The user should, most times, not even notice that their connection has has been managed for them; they should simply see uninterrupted network connectivity.