The warp three engine was a type of warp engine used by Humans in the 22nd century and the Zibalians in the 24th century.
The warp three engine was invented by Humans some time after warp 3 was first achieved by Duvall on the NX-Delta in 2144. (ENT: "First Flight") By 2151 it was possible to upgrade older starships such as Y-class freighters with a warp three engine. Travis Mayweather wondered why the crew of the ECS Fortunate hadn't upgraded, as it would make their ship ten times faster, than its original maximum speed of warp 1.8. A five year cargo run could be cut down to a six month trip. When Keene took back command of the ship, he stated he would need the upgrade to stay in business. (ENT: "Fortunate Son")
In 2364, the Echo Papa 607 planetary defense system, claimed that USS Drake, a Starfleet light cruiser it had destroyed, only had a top speed of warp three. (TNG: "The Arsenal of Freedom") In 2366, the Zibalians still operated freighters, like the Jovis, with a maximum speed of warp factor 3. Within 23 hours the ship could cross a distance of 0.102 light years. (TNG: "The Most Toys")