vasp_std, vasp_gam and vasp_ncl: Which one to use?

I am using VASP 5.4.4. This version (may be earlier version also) has three different executables

vasp_std
vasp_gam
vasp_ncl

But why there are three different executables. Before knowing "why" let us  see how/when to use them properly. 

• vasp_gam is the version of vasp working at the Gamma point only
• vasp_std is standard version of vasp
• vasp_ncl is for non-collinear calculations for instance to perform fully non-collinear magnetic structure calculations or to include spin-orbit interactions in the calculations

Now to why part:

To answer this question, I need some time.

Also see this related post from official forum. 

(this post will be updated further. Keep following this blog).