Mass Effect is one of those sci-fi series with only one fictional technology, and a whole lot of development on that, and on the stories that enables them to tell. And that fictional technology is the mass effect. In Mass Effect there's a fictional element called element 0, or eezo, that humans found out in space. Eezo can alter the mass of other objects when electrically stimulated. Eezo can give a spaceship negative mass and enable faster than light travel. It can reduce the mass of a bullet to almost zero as it's fired from the chamber of a gun, and return it to normal going at an extreme speed. It enables artificial gravity. Humans who are exposed to eezo can gain telekinetic powers. There's a community of aliens out there, and they also use eezo in their technology. There's a ton of politics, philosophical commentary, and secrets out in the galactic community and its history.