Blender 2.8 update available:   Download LapRelax for 2.8: smoothing mesh keeping volume

Blender 2.7:  Download LapRelax: smoothing mesh keeping volume 


This addon implements a smoothing algorithm for meshes based on Laplacian relaxation, but adapted
to have no shrinkage.


First go to User Preferences->Addons and enable the LapRelax addon in the Mesh category.
Go to EditMode, select some vertices and invoke the addon (button in the Mesh Tool panel).
Set the amount of times you want the smoothing operation to be repeated.
The mesh will be smoothed.

If you wish to hotkey LapRelax:
In the Input section of User Preferences at the bottom of the 3D View > Mesh section click 'Add New' button.
In the Operator Identifier box put 'mesh.laprelax'.
Assign a hotkey.
Save as Default (Optional).