Besides the Systems Alliance, there are several other groups that maintain quiet sovereignty in their respective domains. On occasion, you may come in contact with them.
Many times known as "Space Cowboys" these are the Robin Hoods of the night sky. They are the lifeblood of the Black Market and are usually composed of people (or aliens) who live beyond the bounds of the Systems Alliance (and are thus, a constant bother) in the Outerlands. Skilled embezzlers, frauders, forgers, and overall thieves. Although they may appear to be a rowdy bunch, many of them are highly educated and with extensive connections around the planetary system. They tend to generally favor ships that are light and nimble, durable and easy to repair, such as small transport vessels (not, therefore, frigates). Though many Welshers perfer to work alone, most collect in small teams that target particular systems (areas where they are known to gather are dubbed, appropriately, "Welsher Space") or particular types of cargo. Known to work most any job if the money is right, no questions asked. They are mostly nomadic and have a habit of removing surnames, going only by nicknames or first names. Colonello Iancosta was rumored to be in cahoots with them before his servce in the military. Their name comes from the term "to welsh" which suggets the negative connotation of "to take a risk". Gods help you if you ever try to swindle a group of Welshers.
The Turian species are a highly militant alien civilization that claims to be the oldest of all currently living species. They are noted for their strong sense of public service. It is rare to find one who puts his needs ahead of the group. Essentially, any social function that they dominate is one that is sure to have great influence and prowess. Their government is known as the Hierarchy and maintains a meritocratic structure and its members are recognized by their unique facial paint-marks. These, at the top, are known as the Primarchs, who each rule a colonization cluster. The Primarchs vote on matters of national import. They otherwise maintain a "hands-off" policy, trusting the citizens on each level below them to do their jobs competently. The Heirarchy is not in terribly good humor with the human-run Systems Alliance and its democratic structure, and are constantly diplomatic presences in galactic summits, meetings, and especially military matters, if only to veto whatever ridiculous proposal the Alliance has rushed into. Their headquarters are located on the planet Palaven, the Turian homeworld for generations.
Waging a continuous and recondite war throughout the entirety of recorded human history, the Assassin Order, often times known as the Brotherhood, is an organized group of highly-trained assassins who are sworn enemies of the Knights Templar--among other lesser groups. They do not ally themselves with any one group in particular, though from time to time they are called in the shadows by the Systems Alliance for a bit of back up. They do not take any particular sides during times of conflict and are an impartial participant in the various goings ons of the Systems Alliance. They are not particularly fond of CEC due to their due to their affiliations with their main concern, Abstergo. The power-hungry men who run a seemingly innocent pharmeceutical company with their fingers in every pie seek to possess a number of powerful artifacts that could otherwise threaten to turn over every man's mind within the universe when used properly. The assassins seek to stop this, deterring Abstergo agents from obtaining items such as the Pieces of Eden (artifacts of an unknown technology, created by the ever mysterious Those Who Came Before) and the Codices of the Grand Master (which date back to the High Middle Ages).