The Sagittarian Commonwealth is not so much an interstellar government as an economic alliance. They provide a standardized legal framework for trade treaties and contracts, arbitration for commercial disputes, and most importantly a unified currency system for banking. All banks and commercial entities participating in the Commonwealth are required to accept and transfer the standard currency without exchanging to local currency. In most respects, the Commonwealth is treated as a single market, enabling free movement of labor, goods, services, and capital. This means that any Commonwealth citizen may freely move between nations and do business as they see fit with minimal and consistent legal restrictions. In practice, some species are still more "equal" than others.
There are 28 member species in the Commonwealth, more than a dozen of which are humanoid in form. Most of them are minor species who only occupy their home system. Some were included merely to facilitate easy trade lane and refuel access through their home system because laying new altspace network routes was far more expensive. Their unique environments (aquatic, heavy G, small gas giant, etc.) make assimilation into the greater community difficult, so they mostly keep to themselves and trade with passing merchants or sell development rights of their system's resources to others.
The standard currency in the Commonwealth is the Monetary Unit or MU (pronounced 'moo'), leading to many cattle-related slang terms among humans. Banking and purchases are handled almost exclusively via ID card or credentials stored on compies (carried or implanted). The equivalent of loose currency is available through a small number of banks in the form of Certified Monetary Unit Transfers or CMUTs. Pronounced “Cee-Mut”, but often just called Mut(s) and other canine slang references by the lower classes that tend to use them. Similar in shape to a very thin thumb drive (.75 x 1.5 inch), but as thin as a credit card. Electrical contacts similar to chip reader tech on one side, and an e-paper display on the other with the current balance. Heavily encrypted and not worth the herculean effort to hack (usually). Their most common use is for private, untraceable payment, so average people and most governments often assume that people who use them are criminals. Though there is nothing illegal or immoral in the items themselves, they are used for this often enough to keep the stereotype going. Commonwealth merchants and governments are legally obligated to accept CMUTs, but higher class establishments often refuse, sneer, or harass the bearer until they leave without purchase.
Military and Police
SagCom maintains police forces to enforce customs and quarantine and patrol trade routes as a deterrent against piracy, but they do not get involved in military operations and require local government cooperation to operate in sovereign space. It is commonly granted, but politics and jurisdictional clashes are not unheard of. Political and diplomatic pressure is their only legal recourse in those cases, as they are required to step aside in deference to local government. Yes, this is abused, sometimes egregiously. It has even started wars when piracy or other activity was being perpetrated by military or government forces and SagCom units were required to step back and watch it happen without any more interference than reporting the incident to higher authorities. Official SagCom fleets and true military engagements are usually handled by coalitions of member nations brought together to achieve a specific objective on behalf of the entire Commonwealth. Most commonly to defend against outside threats or to enforce a unified response to a member nation that refuses to comply with Commonwealth law.
The official trade language of the Commonwealth is Hestchik, an artificial language designed for ease of pronunciation and translation by as many species as possible.
Generally, most citizens use SagCom to refer to military and police forces and Commonwealth to refer to civilian government.