Workforce management software means scheduling, time and attendance, and labour compliance. It is built for hourly and shift-based teams, and it answers who is working when.
Employee management software is broader and centres on the employee record itself: personal details, contracts, documents and time off, with scheduling or performance added depending on the vendor.
Staff management software is a synonym for the first. People management software usually leans toward the second, plus feedback and goals. Vendors use all four labels interchangeably, so filter on what the tool actually does rather than the word on the pricing page.