requires ‘org.eclipse.core.runtime [3.7.0,4.0.0)’ but it could not be found
If you cannot upgrade to newer eclipse, because of corporate environment for instance, you can install older EGit version, the upgrade is not revolutionary.
Looks like you are installing from eclipse marketplace.
Try installing through “Help->Install New Software..”
use “http://download.eclipse.org/egit/updates-2.1” in update site. it will give you older version of egit that is compatible with Helios.
Make sure to uncheck “Egit plug-in Import Support” – it is not compatible with Helios
About the other items in list you could easily google about Jgit and Egit relationship and about mylyn and its features
Hope this helps