The Vengeance-class frigate was a starship used by Tyber Zann and his criminal organization during the Galactic Civil War.
A Vengeance-class frigate engages its cloaking device in battle.
These ships had the ability to cloak using technology Zann bought from the black market. However, due to a side effect of this addition, the ships possessed no shields. To make up for it, they were equipped with extremely thick armor for protection. However, this extra protection dramatically affected their speed, making them very slow for their class.
Also, these ships were equipped with mass drivers, which bypassed an enemy's ray shields, as well as standard turbolasers. Lastly, Vengeance-class frigates could overheat their cores to self-destruct if the situation called for it.
The Vengeance-class frigates was designed by the Galactic Empire at some point prior to the Battle of Yavin. The Zann Consortium obtained these ships after it raided Bespin. Tyber used the extra tibanna from the raid to design these new ships, using plans he found in the first Death Star's wreckage.
As with the Aggressor-class Star Destroyer, the Vengeance-class shares little with Imperial ship designs, bearing much more similarity with the Zann Consortium ships.