Kuat Drive Yards
EF76 Nebulon-B Escort Frigate

Designed to protect convoys from rebel attacks, the Nebulon-B frigate instead became a popular addition to the rebel fleet.

External resource: Wookieepedia

Known Examples:

Extort: Eighth Imperial Fleet - Active
An Imperial medical frigate during the siege of Farpoint in 48:6.

Free Spirit: New Republic - Active
Ship commanded by Anton Moore during the rebellion.

Nemhain: Rogue Squadron - Active
Assigned to Rogue Squadron as a research vessel in 47:3. To make room for research space, it lacks troop capacity and is only able to carry one starfighter squadron.

Outlander: Rogue Squadron - Active
Captured from the Imperial Union in 51:1 to infiltrate Shedyet.