Modules are custom, dynamic, and if necessary, date-based web applications suited to meet the needs of your website. Modules can be used to build an unlimited number of custom web and mobile applications.
Datatables are database dependent applications that can be formatted for display in a variety of ways on a number of devices. Primarily used for the creation and management of web forms that involve user facing forms, data submission, and retrieval - they can also be used to power mobile apps via API.
Calendars are a type of "Manager" built on top of Solodev datatable functionality that can be modified to create date-based custom applications.
Short codes are the templating language of Solodev that allows you to add functionality and build custom applications without coding knowledge. This allows developers and content editors to work in tandem.