The Star Forge was an ancient weapon made by the Rakata. Darth Pravus once sought out a rebuilt Star Forge, but Nathaniel Kenobi Solo and Jaina Solo Kenobi foiled his scheme. Darth Sarith tried to assemble a new Star Forge that used a Force Harvester as it's primary source of power. Ryas Mor and Kala Zolesa destroyed it, however, and Darth Sarith along with it.
Dark Star Wars Saga
In the dark Star Wars Saga, the Star Forge is not destroyed by the Republic, however, it is atrophied due to both misuse and overuse.