On the far right of the spectrum, we have Software as a Service (SaaS), which is sometimes referred to as on-demand software. SaaS makes cloud-based software available to users over the Internet. With SaaS, everything is provided for you, including the software itself. The only thing you are responsible for is the configuration of the software. Unlike other software pricing models, customers don't have to pay for licenses to use the software. SaaS software is commonly charged using a subscription model based on a timeframe and the number of users.
Examples of SaaS are Salesforce, a customer relationship management (CRM) product, Google's Gmail, Microsoft's Office 365 productivity suite (Word, Excel, PowerPoint, Outlook, OneDrive), and storage solutions such as Dropbox. These are all hosted in the cloud and made available to users without them being responsible for anything other than their configuration.
The software is not installed on the user's own machine, which simplifies both maintenance and support. Technical staff is not required to install, manage, or upgrade the software.