Software as a service

Software as a service (SaaS /sæs/^[1]) is a form of cloud computing in which the provider offers the use of application software to a client and manages all the physical and software resources used by the application.^[2] The distinguishing feature of SaaS compared to other software delivery models is that it separates "the possession and ownership of software from its use".^[3] SaaS began around the turn of the twenty-first century and became the main form of software application deployment by 2023.

SaaS is usually accessed via a web application. Unlike most self-hosted software products, only one version of the software exists and only one operating system and configuration is supported. SaaS products typically run on top of rented infrastructure as a service (IaaS) or platform as a service (PaaS) systems including hardware and sometimes operating systems and middleware to accommodate rapid increases in usage while providing the instant and continuous availability that customers expect. SaaS customers are provided with the abstraction of limitless computing resources, while economy of scale drives down the cost.

There are no specific software development practices that distinguish SaaS from other application development, although often there is a focus on frequent testing and releases. SaaS architectures are typically multi-tenant; although usually they achieve superior efficiency by sharing at least some resources between clients, it is not uncommon to offer a completely siloed environment for an additional fee. Common SaaS revenue models include freemium, subscription, and usage-based fees. Unlike traditional software, rarely is it possible to buy a perpetual license for a certain version of the software.