Tranquiliser guns are weapons built and designed by the Tau'ri. They are non-lethal weapons, as their main purpose is to knock out their enemies alive, so they can be easily captured.
The guns were used to knock out The Touched after they discovered a cure for the disease. They were later used to capture Apophis after encountering him in the Nox homeworld. However, the darts failed to pass Apophis' personal sheild. Later, when Hathor took over the SGC by controlling the men in the base, Carter and O'Neill used the guns to knock out the SFs guarding her. (SG1: "The Broca Divide", "The Nox", "Hathor")
Tranquiliser darts are capable of piercing the armor of a Kull warrior. However, the warrior's physiology made it impossible for the warrior to be knocked out. (SG1: "Evolution, Part 1")
When Osiris traveled to Earth to probe Doctor Daniel Jackson's mind, he figured out her plot and a plan was set up to use the tranquilizer guns to knock her out so she could be safley removed from her host Sarah Gardner. In the skirmish that followed, despite Osiris using a personal shield, O'Neill managed to tranquilze her from behind and Osiris was succesfully removed from her host. (SG1: "Chimera")