(covers information from several alternate timelines)
The shuttle was capable of achieving a speed of at least warp 6 and was equipped with deflector shields. It was also equipped with several advanced anti-Borg technologies developed by the crew of USS Voyager between 2394 and 2404, including stealth technology, an ablative armor generator, transphasic torpedoes, as well as a neural interface and synaptic transceiver.
Along with the anti-Borg technology, she equipped the shuttle with a chrono deflector stolen from Korath in 2404. The shuttle was chased and fired on by his forces, but escaped only to be intercepted by the USS Rhode Island. Its captain, Harry Kim, allowed Janeway to leave and rescued her from Korath's forces when they caught up with them.
Janeway was then able to generate a temporal rift to the Delta Quadrant of the year 2378, where she shared the technology with the crew of Voyager. Later, she used the shuttle to infiltrate the Borg Unicomplex and delivered a neurolytic pathogen to cripple the Borg Collective. This bought time which allowed Voyager to use a Borg transwarp conduit to return to the Alpha Quadrant sixteen years before they would have without Admiral Janeway's intervention. The Borg found the shuttle eventually and it was captured, however the unicomplex was destroyed soon after, so its technology wasn't assimilated. (VOY: "Endgame")
According to the script, this vessel was described as a "futuristic Starfleet shuttle."
According to a production sketch of this shuttle by Rick Sternbach, dated February 2001, the SC-4 was an "uprated Type-18H shuttle". It had nanotech molecular armor plating, hot-ready filament phasers, and conformal defense shield grid (embedded). 
The interior of the shuttlecraft was a set that was filmed on Paramount Stage 16. (Information from shooting schedule)