Star Wars: Interregnum is an upcoming mod for Sins of a Solar Empire: Rebellion that builds off of the highly successful Enhanced 4X Mod. Fleeing the unknown terror that is chasing the Vasari, the factions of Sins of a Solar Empire stumble on a temporary wormhole that takes them to a galaxy far, far away. The sudden arrival of armadas with trillions of refugees and thousands of warships between the events of Episodes 5 & 6 forever alters the Star Wars universe and plunges the galaxy into an unprecedented period of chaos and violence. Begun, a new conflict has.
My personal favorite Starfighter of all time is the Alpha-class Xg-1 Star Wing, commonly called the Assault Gunboat. Produced by Cygnus Spaceworks, the same designers of the Lambda class Shuttle and Sentinel Class landingcraft, it was one of the Empire's first starfighter designs with shields and a hyperdrive that could compete with Rebel fighters one on one. In Interregnum, it serves as a versatile bomber capable of damaging many types of targets with its laser cannons, ion cannons and light warhead launcher. However, it cannot be easily deployed, as they can only be produced by an ability on the ISD-I or from the Executor titan.
in which movie do we see it?
None, it first appeared in the TIE Fighter video game. Since that is safely before Episode 6 I see no reason why the chaos in the EU would have any impact on it. And even if it does, I don't really intend to pay attention to any of that.