How to get the surface mesh of an volume mesh?

Hello everyone,

I got a question and would like to post it here.

Suppose we have a volume mesh, I am interesting in obtaining surface elements or the surface mesh of this volume mesh. 

Does anyone here know a free source tool to do this?

Or put in another way, is there a mesh generator that can generate a volume mesh exactly based on a user-defined surface mesh?

I know this can be done in Abaqus by mouse picking the surface of interest.

However, I am looking for a tool that I can use for free. 

Thank you very much for any information.

Rong