Software as a Service (SaaS) provides users access to fully managed applications hosted in the cloud. CompTIA A+ explains that SaaS is subscription-based and typically billed monthly or annually, which aligns perfectly with the phrase “recurring fee.” Business productivity applications—such as Microsoft 365, Google Workspace, Zoom, Slack, and Salesforce—are classic examples of SaaS offerings.

SaaS applications run entirely in the provider’s cloud environment, eliminating the need for installation, maintenance, or management by the customer. This makes SaaS ideal for businesses that need reliable, scalable tools without maintaining their own infrastructure.

DaaS (Desktop as a Service) provides virtual desktops.

PaaS (Platform as a Service) offers a development framework for building applications.

IaaS (Infrastructure as a Service) provides virtual servers, storage, and networking—not end-user productivity apps.

Thus, SaaS is the correct and only model that matches the description of subscription-based access to productivity applications.