Extensible software-as-a-service computing platform

Technologies are provided for an extensible software-as-a-service (SaaS) computing platform. In some embodiments, a computing system includes computer-executable components comprising multiple core modules that provide a defined service. The multiple core modules include at least one extension point corresponding to a first core module of the multiple core modules, where a first extension point of the at least one extension point has a tenant-specific extension module mapped thereto that customizes the defined service. The computer-executable components also can include an application programming interface (API) corresponding to a defined tenant. The computing system also includes a data model corresponding to the defined tenant. Tenant-specific extension modules mapped to the at least one extension point can customize the API and/or the data model.