Difference between Eclipse Europa, Helios, Galileo

The Eclipse (software) page on Wikipedia summarizes it pretty well:

Releases

Since 2006, the Eclipse Foundation has coordinated an annual Simultaneous Release. Each release includes the Eclipse Platform as well as a number of other Eclipse projects. Until the Galileo release, releases were named after the moons of the solar system.

So far, each Simultaneous Release has occurred at the end of June.

Release         Main Release   Platform version      Projects
Photon          27 June 2018     4.8
Oxygen          28 June 2017     4.7                 
Neon            22 June 2016     4.6                 
Mars            24 June 2015     4.5                 Mars Projects
Luna            25 June 2014     4.4                 Luna Projects
Kepler          26 June 2013     4.3                 Kepler Projects
Juno            27 June 2012     4.2                 Juno Projects
Indigo          22 June 2011     3.7                 Indigo projects
Helios          23 June 2010     3.6                 Helios projects
Galileo         24 June 2009     3.5                 Galileo projects
Ganymede        25 June 2008     3.4                 Ganymede projects
Europa          29 June 2007     3.3                 Europa projects
Callisto        30 June 2006     3.2                 Callisto projects
Eclipse 3.1     28 June 2005     3.1  
Eclipse 3.0     28 June 2004     3.0  

To summarize, Helios, Galileo, Ganymede, etc are just code names for versions of the Eclipse platform (personally, I'd prefer Eclipse to use traditional version numbers instead of code names, it would make things clearer and easier). My suggestion would be to use the latest version, i.e. Eclipse Oxygen (4.7) (in the original version of this answer, it said "Helios (3.6.1)").

On top of the "platform", Eclipse then distributes various Packages (i.e. the "platform" with a default set of plugins to achieve specialized tasks), such as Eclipse IDE for Java Developers, Eclipse IDE for Java EE Developers, Eclipse IDE for C/C++ Developers, etc (see this link for a comparison of their content).

To develop Java Desktop applications, the Helios release of Eclipse IDE for Java Developers should suffice (you can always install "additional plugins" if required).

Each version has some improvements in certain technologies. For users the biggest difference is whether or not to execute certain plugins, because some were made only for a particular version of Eclipse.

To see a list of the Eclipse release name and it's corresponding version number go to this website. http://en.wikipedia.org/wiki/Eclipse_%28software%29#Release

• Release Date Platform version
• Juno ?? June 2012 4.2?
• Indigo 22 June 2011 3.7
• Helios 23 June 2010 3.6
• Galileo 24 June 2009 3.5
• Ganymede 25 June 2008 3.4
• Europa 29 June 2007 3.3
• Callisto 30 June 2006 3.2
• Eclipse 3.1 28 June 2005 3.1
• Eclipse 3.0 21 June 2004 3.0

I too dislike the way that the Eclipse foundation DOES NOT use the version number for their downloads or on the Help -> About Eclipse dialog. They do display the version on the download webpage, but the actual file name is something like:

• eclipse-java-indigo-SR1-linux-gtk.tar.gz
• eclipse-java-helios-linux-gtk.tar.gz

But over time, you forget what release name goes with what version number. I would much prefer a file naming convention like:

• eclipse-3.7.1-java-indigo-SR1-linux-gtk.tar.gz
• eclipse-3.6-java-helios-linux-gtk.tar.gz

This way you get BOTH from the file name and it is sortable in a directory listing. Fortunately, they mostly choose names are alphabetically after the previous one (except for 3.4-Ganymede vs the newer 3.5-Galileo).

Those are just version designations (just like windows xp, vista or windows 7) which they are using to name their major releases, instead of using version numbers. so you'll want to use the newest eclipse version available, which is helios (or 3.6 which is the corresponding version number).