Software Integration ?

Usually in a complex software development; various modules of the software are distributed among software developers;  after completion of development who is responsible to integrate individual modules and which tool is used to manage it?

Yes. Different modules are developed by different programmers. After developig, testing of modules is done by programmers first. Then quality engineers also test each module. After testing of these modules, system is integrated and then tested again as a single application. This integration is responsibility of programmers. Several tools are used in industry to integrate system. Some examples of such tools are FileZilla, cuteFTP and winSCP.