The Acarr System was the former home of Clan Plagueis after the unification of Clan Exar Kun and Clan Satal Keto. The clan lived here for half a year before the star started to go supernova. They left just in time, as the star exploded and destroyed the system for all eternity.
Acarr
The Acarr System was first at the very beginning years of the Old Republic, as part of a routine survey mission to find possible avenues of expansion of the ever increasing population of the Republic. At first the system seemed promising to the explorers as it provided an unused canvas for them to terraform and populate as they wished. The plans for expansion, however, were cut short when the charting ship mysteriously vanished in the middle of a transmission. A follow up ship found the remains of the former ship scattered throughout the star system, along with the cause of its destruction: random ionic solar blasts. The yellow star of Acarr, it was discovered, was in the early years of transitioning into a red giant, and was releasing random bursts of ionic solar flares that wrecked havoc to both ships and guidance systems. To make matters worse, the flares had attracted the attention of space dwelling organisms later named Acarrian Terragots.
These creatures were as large as an average escort ship, and their natural habitat had given them armor just as strong, which combined with the radiation blasts them seemed to emit, fueled by the radiation from nearby stars. The Terragots were territorial and agressive, and took offense to any intrusion into their territory. The plans for colonization by the Old Republic were scrapped.
Hundreds of years later, when the Dark Jedi Brotherhood split from the Emperor's Hammer, Battlemaster Khan discovered that the system had gone unused, and set his sights on using the system to house his "fugitive" Clan Alvaak. The Terragots proved no challenge to force sensitive dark jedi, and the Acarr System became the home of Clan Alvaak.
Years pasted, and the system was given over to Clan Exar Kun. When the clan combined with another, the new clan, named Clan Plagueis, took over the system. They stayed here as long as they could, but were forced to relocate when the main star moved into its final stage and went super nova. Today, the entire area where the system used to stand is one huge black hole
Sigil
The closest orbital to the sun, Siligan, simply named Sigil, is a massive gas giant that serves as a natural buffer between the outer planets and the radiation of the sun. This buffer failed, of course, when the star went supernova. It is also the natural resting spot of the Terragots.
Eden
Eden is the former homeworld of House Bane, and was perfect space for the secretive, information gathering and hording house to store their knowledge of information.The tropical sorroundings discourage visitors, as do the insects and animal life, but the Krath learned to keep these things at bay, and formed a relationship with the locals to get supplies in exchange for protection, despite the natives thinking of the dark jedi as demons.
After the planet was abandoned, Battleteam Exar's Shadow, led by Aabsdu, investigated it for any traces. While they found nothing useful to the clan, they did uncover remnants of the Crimson Tide, and eventually the capture of Alonzo Bodelle
Ysgard
Ysgard was a dead planet that use to serve as the capital planet when under rule of the Alvaak. During Clan Plagueis' rule, it was used as a mining colony for its ore and minerals.
Elysian
A desert planet, it was the homeworld of House Exar Kun due to its open plains perfect for flying. It was also full of silicon that was mined for fighter fuel. Due to its central orbit around Acarr, it was also a perfect planet to house military in order to protect the system.
Battle Team Blades of Kun once investigated the planet after receiving a warning distress signal, but nothing was discovered before they were forced to evacuate.
Haven
The former homeworld of House Satal Keto, Haven was perfect for training grounds and barracks. It provided plenty of food and other nessecities, and was perfect for Dark Jedi training. It was also clear of any terrible atmosphere, so it was easy to watch from the surface for invaders.
Byfrost
Being the furthest from Acarr, Byfrost was a frozen ocean world where all life existed beneath the ice. In order to breat, organisms had to break small holes in the ice, extracting oxygen from the water, or dieing. A single settlement existed on the surface that monitered all incoming and outgoing transports and vessels. When Clan Plagueis moved to the system, the planet was chosen as the clan capital for its privacy, and Castle Frost was erected on one of the large icey plains