The Star Forge, one of the many forms of The Composer, was the home of Darth Malak during The Rise of Trask Ulgo, and was his base of operations for his nefarious deeds. It was also the residence of Bandy before his death at the hands of Trask Ulgo .
It can drain the powers of stars and use the energy to create fleets of warships. Somehow. It can also make armies of pathetic droids or create loadsa weapons. The Star Forge was destroyed by a Republic fleet during the Rise of Trask Ulgo and was thought gone forever. However, the plans were soon discovered by the Protheans, who began its construction once again.