Volume Preserving Smoothing takes also into account sharp edges – they will be treated as rails for verts to slide on. This can help to maintain main shapes of smoothed object.

To access the smoothing menu use W key in mesh edit mode -> Mesh Smoothing:

Inflate smoothing
Laplacian HC smoothing
Volume smoothing
Additional parameters are available after executing operator with F6 hotkey.

Since 2.3 update here is now smoothing brush Tool located at the bottom of left Toolbar (N).

To make edge into rail edge – just mark edge loop as sharp. Now verts belonging to this edge, will move only along edge.

Features:
smooth mesh while maintaining main object shape
border mesh vertices will slide along border edges, without shrinking (or they can be frozen)
center vertices wont move away from symmetry X axis line
works with shapekeys
ability to define sliding rail edges (marked as sharp)
three edge tension methods (Uniform, Proportional to edge length, Inverse to edge length)
optimized with NUMPY

Downloads: pls buy & support the dev!

Filename: Volume_Preserving_Smoothing

Recommended link below => FULL SPEED.

https://upload.ac/icz8a7fjwnjd

if theres no file extension like .zip or .rar then dont worry just right click on it and click decompress it will work. 7-zip is recommended. it always works fine.
above links dead? use these mirrors below! also includes zippyshare + openload links!

https://mirrorace.com/m/Vdjt