Abstract. This paper explores modern open-source cloud platforms giving insight into the theoretical concepts they are based on, along with the analysis of challenges they face when deployed in business environment. In the first part of the paper, theoretical concepts like cloud computing, virtualization and software as a service paradigm, which form the basis for this new concept – the SaaS cloud platform, are discussed. Afterwards, the analysis of performance and deployment issues of the two most prominent open-source platforms Ulteo and LTSP Cluster is presented. We also discuss proposed solution to the issue of user application profile persistence between sessions.