Are you sure they are transfers? Since they are just "mock ups" and not actual photographs of t-shirts, it's impossible to say what printing method would be used.
Most likely it's just regular screen printing directly on the garment.
It's not vinyl (because it has gradients) and it's not sublimation (because it's on a dark colored shirt) and it's not probably not laser.
As for the software used to create the design, it was probably a professional artist that could use any software to create a high quality design. Any of the software recommendations posted here would work:
http://www.t-shirtforums.com/tags/best-software/