From BlenderWiki
Blender 2.40 Release Notes
The Blender Foundation and online developer community are proud to present Blender 2.40!
Blender has had another long development cycle resulting in a release
packed with rewrites, new features and improvements. The major additions this release are the Character Animation rewrite, the added Fluid Dynamics system, improved editing and rendering of Particle Based Hair, and the Modifier Stack.
Here are the links to the wiki pages of interest.
Blender 2.40 release news
All the 2.40 release news from different websites. Feel free to add one.