Clusters built with off-the-shelf workstations/PCs and off-the-shelf high bandwidth networks are being used for hosting a diverse spectrum of demanding applications. Our research has been examining numerous architectural, systems software and application level issues in this environment. In contrast to many other projects addressing similar goals, our focus has been on examining issues that arise when there are several users/applications concurrently executing on the cluster. These issues (scalability, Quality-of-Service, interference between users, etc.) are extremely important for today’s multi-user time-shared server environments that clusters are deployed in. Further, we are also examining new and emerging applications for clusters whose requirements can be significantly different from those posed by traditional scientific applications.