Eclipse is developed as a modularized system with a central core platform and additional features and plugins that provide functionality required for a certain language (like Java or C++). These packaged versions of Eclipse that are put together for different languages is what is provided on its download page.
You may feel that the Eclipse packages available for Java or C++ (CDT) are extremely bloated with hundreds of features and plugins that you may never use. For example, Eclipse CDT includes hundreds of MyLyn features and cross-compiler support, none of which I may require right now. The beauty of Eclipse is that everything is a plugin, so you can actually build yourself a lean Eclipse that only includes what you want. This way you can build a minimal Eclipse that has only the features you want.
The core of Eclipse is provided for download as Eclipse Platform Runtime Binary. To get it, go to this page and click on the build number you want. It opens a new page, where you scroll down to the section named Platform Runtime Binary and download the package matching your system.
Unzip the zip file you downloaded and run the
eclipse binary file. The IDE opens and it works.
Now add the plugins you want from Help -> Install New Software. For plugins provided by Eclipse, choose Luna from the dropdown. For external plugins, add their URL.
For creating a Eclipse C++ IDE of my own, I installed these plugins:
For creating a Eclipse Python IDE of my own, I installed these plugins:
Tried with: Eclipse 4.4.2 and Ubuntu 14.04