This paper presents a concept for an e-Science oriented opportunistic cloud computing service with QoS assurances, as an infrastructure to offer to researchers computing resources with the flexibility and ease of use of a cloud computing service, supported through the opportunistic use of the idle computing resources available in academic institutions, with mechanisms in place to address the low reliability of these opportunistic resources. Also we present the work done in the context of the UnaCloud project, the experiences with the use of the tool to support real research projects, the existing perspectives for current and future work on this project, related work, and the significance of this project in the regional research community.