Splatsch: "Nova Mod"
May I ask, what's the difference between "Reality Mod" and "Emperor Wars" ?
Reality is probably best described as a continuation of Vanilla, with a little extra lore flavor from the sourcebooks, and a big emphasis on the whole 'climb out of the Dark Age' schtick. Its biggest change by far is that Factories take 10 turns to build, and cost a lot of resources, many of which are locked behind tech that takes a while to unlock. It is a slow-burn mod.
Emperor Wars I believe started as a mod of Reality, but it took things a step further regarding the lore from the fluff. So instead of each Major House starting with only one planet, the Known Worlds are divided up among the major houses (and the League, and the Church). It also does a drastic overhaul of units and technology, adding a TON of special units. But by far the biggest change is that most of the Known Worlds are divved up and you start off with a lot more going on than in vanilla. Its primarily designed for Multiplayer and to let people jump right into action instead of having the slow expansion of vanilla.