In-system couriers were small Federation Starfleet vessels in use during the late 24th century. They were precisely calibrated for high warp factors within the gravitational fields of specific star systems, but even then were generally only used in emergencies due to the hazards of in-system warp travel. The expense of this highly specific use meant that they had an extremely short range and very few amenities.
In 2368, Special agent Gariff Lucsly used one of the Sol System's in-system couriers, commanded by a Starfleet lieutenant, to travel from Earth to Eris. He hoped to prevent some of the time-displaced Bozeman's crew from accessing the Eridian Vault and using some of the time travel devices stored there to return to 2278. (DTI novel: Watching the Clock)