The T-Spheres are weapons invented and used by Curtis Holt. The spheres have several uses such as self-targeting projectile.
The spheres were originally intended for Felicity Smoak's program for "prototypes for the future" while still working at Palmer Technologies. After Curtis quit the job and joined Team Arrow as Mr. Terrific he continued working on the spheres in order to help him fight crime. Although at first they were not functional, by the time the team encountered Vigilante, he used them successfully to knock him out.