Software-as-a-Service (SaaS) often adopts multi-tenancy architecture (MTA). However, building a MTA SaaS application requires significant effort, either from scratch or using existing platforms such as Force.com or Google App Engine. This paper introduces EasySaaS - a SaaS development framework designed to simplify SaaS development. EasySaaS provides two alternatives to build a SaaS application. First alternative allows tenants to publish their application specifications with their requirements, as well as test scripts and let the SaaS providers customize their SaaS solutions to meet tenants' requirements. The second alternative allows tenants to compose the application using templates provided in EasySaaS. This framework alleviates the workload of tenant developers, and provides an easy approach for customization according to tenants' requirements in a collaborative manner. Most services in the platform is domain independent as the domain knowledge are stored in ontology to support cross-domain development.