ActOnAll is a test (not in the molecuilder source tree, but as a singular UnitTest) to get a template function for Vector member function calls.
The idea is to have a call such as:
ActOnAll( AddVector (1.,0.,0.) );
which performs the AddVector on all Vectors (inside the atoms) in e.g. the molecule class.
This would save a lot of unnecessary lines and would make the code in general easier to read.