We present the e-Clouds project aimed at allowing researchers to easily execute many applications on public Infrastructure as a Service (IaaS) solutions. Designed for being a Software as a Service (SaaS) marketplace for scientific applications, e-Clouds allows researchers to submit jobs which are transparently executed on public IaaS platforms, such as Amazon Web Services (AWS). e-Clouds manages the on-demand provisioning and configuration of computing instances, storage, applications, schedulers, jobs, and data. The architectural design and how a first application has been supported on e-Clouds are presented. e-Clouds will allow researchers to easily share and execute applications in the cloud without the complexities associated with details of IT configurations and management. e-Clouds provides new opportunities for research groups with low or none budget for dedicated cluster or grid solutions, providing on-demand access to ready-to-use applications and accelerating the result generation of e-Science projects.