The Arduino ecosystem including it's boards, tools, SDKs and libraries make it super easy for hobbyist computer engineers to build electronic projects that incorporate pretty powerful microcontrollers and an environment to program those microcontrollers.
The Arduino IDE from arduino.cc provides a simple IDE that lets these hobbyists get started. However, it is really simple. As projects get bigger and more complex, Arduino developers need something more powerful. They need an IDE that supports pure C++ development with content assist and source navigation the professional developers take for granted.
The Eclipse C++ IDE for Arduino (formally Arduino C++ IDE) is a set of plug-ins that provide a professional, yet easy to use development environment for Arduino programming that leverages the power of the industry leading Eclipse CDT. Building on Eclipse, the Arduino programmer can learn important skills and take advantage of the larger Eclipse ecosystem to build true Internet of Things projects that span from their microcontrollers to the cloud.
This is the new release for Eclipse Neon. There are number of changes since the preview release in Mars. The main one is the new Arduino Downloads Manager which is available in the Help menu and is used to download board platform SDKs and libraries. This replaces the preference page that did that previously.
Note for users of the Arduino C++ IDE preview, it's probably a good idea to delete the .arduinocdt directory from your home directory as the layout of the install has changed a little. You can then use the new Arduino Downloads Manager to install the platforms and libraries you were using.
An instructional video on how to install and use the Eclipse C++ IDE for Arduino is available on YouTube.
As the Arduino C++ IDE is a part of the Eclipse CDT project, please visit the CDT forum for any questions you may have. Also file any bugs in the CDT bugzilla area under the component cdt-arduino. This is still considered a Beta though I'm not sure too many areas yet we don't support. But please, if you see anything, let me know and I'll fix it as soon as I can.