As mentioned before, the interface supports multiple users and groups. Thus, a single server can allow many researchers to perform calculations from their web browser, without having to install any software on their personal computer. Moreover, users in the same group can have access to other member's projects (unless marked as "private", in which case they are hidden and inaccessible). In this way, users can collaborate, provide assistance, and learn from each other and leverage others' calculations as starting point for their own. Calculations of users in a group cannot be viewed by users outside of the group, in order to protect potentially confidential or sensitive data. This structure enables a single CalcUS server, if installed on a computer accessible network-wide, to be used by as many research groups and users as desired (Scheme 2). If many calculations are submitted locally to be performed on the server, they will be queued and performed sequentially through the task manager. The execution of calculations submitted to remote HPC resources will be managed by each cluster's queueing system. Consequently, the number of end-users is only limited by the power of the server host and by the amount of computational power required by them. If the server is only used to manage remote calculations on HPC clusters, however, a very large number of end-users can be supported. Scheme 2. User structure.