Characters start out on Earth, much like our own but conquered by an alien force using magic and technology together. Travel to other world can be accomplished by spacecraft with enchanted transit systems, but purely magical travel is often faster and more convenient. While any sort of campaigning is possible, the default is to have characters taking mercenary jobs from The Firm, they don't actually work for The Firm as employees, but act as independent contractors with the Firm guaranteeing pay when the job is completed. In uncivilized areas you can pretty much do as you please, but in advanced locations races often considered monsters are likely citizens.
The rules are based on D6, but to provide a rich selection of creatures and magic those are converted from D20 (Pathfinder mostly, but other D20 sources as well). While there will be lots of notes on conversions elsewhere what it really means is characters will start at mid-level competence and advance slowly. Monsters of all challenge ratings can be faced (or not faced) at any time.
In the current campaign the characters work for The Firm, often doing extra side work along the way, and have quickly escalated from small local work fighting a small street gang to assassinating world leaders and traveling to other planets to recover rare artifacts.