Federation Merchant Marine
The Federation Merchant Marine, or FMM, was an organization created with the intent to facilitate trade and the growth of the Federation Economy.
The basic idea behind the FMM was that a civilian ship such as a Freighter or Transport was very expensive, and the ordinary civilian would probably never be able to afford one. So the government, under the guidance of the Federation Trade Commission or FTC, would build and operate a merchant fleet, the FMM.
Essentially, FMM vessels, initially the freighter FSS Neon and the transport FSS North Star were built with the intent that they would be manned by crews trained by the FTC and would provide transportation services for civilian companies. Later, these companies were able to lease the FMM vessels directly from FTC.
The problem with FMM was that for several years, the TOS Econ system did not really exist. It came online in 1996 around the same time as the current version of space. Even after Econ came online, it took quite a while to get the Empire geared up for trade and economic production. As a result, for several years there was no clear purpose for the FMM, and it moved off in certain non-economic dimensions.
Essentially, the FMM, or the FMM/FTC, as most people thought of the two as a single organization at the time, became civilian explorers and adventurers. Under the leadership of Gavelin Brody, who had left StarFleet due to a conflict with his academy instructor, Zac LeVasseur, the FMM became a vibrant and large organization of quasi-military adventurers. After StarFleet's player ranks were decimated by the destruction of the USS Yorktown, the FMM began to present itself as an alternative military organization (many of its members interpretted the organization's name to mean that they were "Marines", as in a rapid-deployment amphibious combat force, rather than a "Merchant Marine", a group of merchant trade vessels) and became larger and more popular, for a time, than StarFleet.
During this time an intense rivalry developed between StarFleet and the FMM. FMMers referred to StarFleet as 'TwinkFleet', while SFers called FMMers glorified truck drivers.
Eventually, the efforts of one particularly renowned StarFleet captain and later Fleet Admiral rebalanced the scales in StarFleet's favor. FMM was pressured to accept its nonmilitary role, and as the Econ began to develop its players were steered more toward their original purpose. This made them less able to compete with StarFleet on an adventure level. What's more, when this renowned officer saw the opportunity to bring Gavelin Brody back into the Fleet, he took it, and Brody brought with him some of the best players from FMM/FTC.
After that time FMM went into something of a decline, and became a smaller organization, clearly civilian in nature and clearly geared toward trade. The lack of regular trade with other empires hurt it considerably. Also, the FTC was separated from the FMM, and FTC personnel were given the task of overseeing and training FMMers, who were then more or less free agents.
With the galaxy changing and the inter-empire trading which had helped sustain the FMM becoming a thing of the past, the Merchant Marine lost its important spot in the Empire economy. Much of their old business was taken over by smaller, rising companies, and the Merchant Marine eventually dissolved into the ether which so many other failed businesses in the Federation eventually fell into.