When Salesforce started selling a CRM in the cloud, they were the first and only SaaS company.
Salesforce essentially invented the free trail and a new model for selling software. The product was a software-as-a-service product delivered over the cloud, which created a powerful viral distribution channel among these early users. Since the product didn’t require any setup, it was technically possible for Salesforce to offer the tool for free. So they created a plan where the first five users at any company could use the CRM free of charge.
Once a team member tried it and liked it, scaling up the team was easy thanks to Salesforce’s straightforward pricing plan. They could scale up by seat or by upgrading to more functionality. Giving customers two ways to expand also helped fuel geometric revenue growth for Salesforce.
Later Salesforce transformed is business and became a Platform as a Service by opening up it's app for third party developers with the Salesforce ApExchange