Work types and modules are an integral part of the project hierarchy in Intervals.
Modules are typically used for a phase of a project or for a feature being developed. They are “categories” where time and tasks are attached for reporting and for management. For example, say designing a logo can be placed in a Design module. This allows you to run filters (even across different projects) to see which tasks are in the design module as well as run reports on time for that module as well.
Work types are service categories that can be applied to a time entry when it is entered in the system. Since work types carry an hourly rate with them, when you run reports you can see the type of work that was performed for the task as well.
To give another example, say you have a task to create an initial design specification. While working on that task you could potentially have project management time, design time, meeting time, etc. When running reports you can see the type of work that was performed for the task as well as the financial value of the work.