Eclipse SDK 4.1 is a major release of the new Eclipse platform harvested from the technologies worked on in the E4 incubator project. The first release (4.0) appeared on July 28, 2010, and is based on content from the Helios simultaneous release. For more information see the Release Landing Page and the FAQ. The second release (4.1) was released on June 22nd, 2011, in line with the Indigo Simultaneous Release.
This is a high-level overview of what the Eclipse 4.x SDK consists of. You will notice that most of the functionality (the Java tooling, for example) is exactly the same as what was released with Eclipse 3.6: