At its core, castellum can be used to record which subjects have participated in which studies. This allows to keep track of all data related to a subject, e.g. to export or delete all of it on request.
It is possible to find potential subjects for a study from the pool of subjects that have been entered into castellum. They can then be contacted either manually or automatically via email. Subjects are only considered if they have given consent to recruitment and if their recruitment attributes match the filters that have been defined in the study.
Castellum can be used to manage appointments for test session. It will send reminder mails to subjects automatically. You can also define resources such as rooms or machines.