Delmak, a technologically advanced planet of modern cities and air travel, was conquered by Sokar and became the home planet for his forces. It was orbited by Netu, the moon transformed into a prison designed to resemble Hell, until Netu's destruction. After Sokar's death, Apophis escaped from Netu to Delmak and made it his home base until his Replicator infested mothership was sabotaged by SG-1, sending him crashing into Delmak's surface.
The features of Delmak were also visible on the world on which Anubis established his base of operations following his return to human form. There he met with Ba'al and prepared to carry out his plan to use the Ancient weapon of Dakara to wipe out all life in the galaxy.
Cross Reference: Apophis, Netu, Sokar
Episode Reference: Jolinar's Memories, The Devil You Know, Enemies, Reckoning, Threads