The Utopia Planitia Shipyard, found logically enough at and above Utopia Planitia, is Starfleet's main manufacturing center. There the UFP builds practically everything they don't buy from other Fen, from tools to the modules for their starbases to their most prominent product, starships. They are a vast, sprawling complex of warehouses, factories and workshops that dominate the Utopia Planitia settlement, and whose cavernous maw Port Phobos exists to feed.
The Yards are not exclusively the dominion of the Trekkies, though they are the dominant faction. Gearheads (from VOTOMS and Gundam fen to NUNS) and many independents have smaller facilities or shops, producing their own products and taking advantage of the industrial infrastructure present. Also due to the presence of the yards, the local Starfleet Academy Campus has the largest Naval Architecture and Aerospace Engineering departments in Fenspace.
In addition to exporting a large percentage of the manufactured goods in Fenspace, the Yards often do contract work for other factions, or even individual fen. Contracted ships and other things don't have to be Trek themed, but those handwaved items coming out of Federation-run facilities tend to have Trek-related quirks.
Probably the most famous collaboration the Yards have been involved with was the development and construction of the Gagarin-class explorers in association with the Soviet Air Force in Exile.