As of my last update in September 2021, there were several popular ATS (Applicant Tracking System) software providers in the USA. Some of the best ATS software options at that time included Workday, Greenhouse, Lever, Bullhorn, iCIMS, and JazzHR. However, please note that the ATS landscape can change rapidly, with new entrants and improvements to existing systems. To find the current best ATS software for your needs, I recommend conducting thorough research, reading reviews, and considering factors like user-friendliness, integration capabilities, cost, and customer support.