Stratos is multi-tenanted. In other words, there are many tenants. Each tenant generally represents an organization and isolated from other tenants, where each tenant has his own users, resources, and permissions. Stratos supports multiple PaaS services. Each PaaS service is actually a WSO2 Products (e.g. AS, BPS, ESB etc.) offered as a service. Using those services, tenants may deploy their own Web Services, Mediation logic, Workflows, and Gadgets etc.
Read the full blog post at Srinath's Blog