With the popularization of cloud computing, several enterprises and open-source communities have developed their own cloud solutions. A number of factors weigh on user selection, as each one has peculiar characteristics and may target different usage scenarios. Considering such challenge, this paper focuses on giving the reader an understanding of some major existing open cloud computing solutions – XCP, Eucalyptus and Open Nebula. Hopefully, a deep comparison of such solutions can leverage the cloud computing research area providing a good starting point to research groups and interested readers.