The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Our recent first data release (XCS-DR1) contains 503 optically confirmed groups and clusters, among which 256 new to the literature and 357 whose X-ray emission was detected for the first time. We discuss their properties and provide an update on the work being done. As examples of the applications of XCS-DR1, we mention the 17 fossil groups/clusters identified with the help of the Sloan Digital Sky Survey. Their brightest galaxies have stellar populations and star-formation histories which are similar to normal brightest cluster galaxies, but their stellar masses are significantly larger and correspond to a much bigger fraction of the total group/cluster optical luminosity. We also highlight the 15 clusters expected tobe also detected by the Planck satellite, and characterize the expected overlap between the final XCS and Planck cluster catalogues.