I would like to gain knowledge on available free or commercial tools to generate automatically structured mesh from geometry, particularly quadrilateral.
Which options do I have ?
Permit me to clarify - you ask about "structured mesh" that's "quadrilateral." By definition, a structured mesh (or grid) consists of quads (2D) and hexes (3D). So I want to clarify that you're inquiring about automatic structured quad/hex grid generation.
If so, you're seeking the holy grail. While there are many software tools for generating structured grids the degree of "automation" varies greatly. I put automation in quotes because exactly what is meant by automation depends on who's asking. (To not digress too much, Fred Brooks in his book The Mythical Man Month wrote that automatic has always been a synonym for "better than we're currently doing.")
When I think of automatic grid generation I do so in the literal sense. You have software into which you import a CAD geometry, maybe you specify a handful of meshing parameters, you press a button, magic happens, and a grid pops out the other end. (The other problem with automation is people mean "make a grid automatically and exactly the way I would've made it manually.")
CUBIT is always the first thing that comes to mind when thinking about automatic hex generation. However, it doesn't always generate a structured hex grid - it uses many techniques that generate unstructured hexes. As you'll learn when you Google it, CUBIT is a U.S. Dept. of Energy product that has been commercialized as Trelis. Also, I was told of a plan to release CUBIT as open source.
GridPro is a commercial tool for structured grid generation that has cool technology for doing what many consider to be the hard part of structured hex grid generation - the decomposition of the 3D domain into zones or blocks.
You don't specify your intended area of application. CUBIT, for example, seems to be more for structural mechanics. The other two packages I mention are more for CFD. The requirements of the analysis will dictate which features are important to have in an automatic gridder.
Hope this helps.
Otherwise, there are too many structured grid generators of all sorts (commercial, government, academic) to list here. Google is your friend.
gmsh is a viable way to generate quadrilateral meshes in 2d. It's also open source.