OneBox OS allows to create your own interface fields. For example, if the standard fields are not enough for you, you can create your own and add it to the workflow interface.
To create an additional field for the process you need to:
Open any app associated with processes, for example "Tasks":
Choose the "Additional fields" option:
Click on "Add a field" button:
Specify the field's name and its type:
Click on "Insert a new record":
Additional field has been created, now you need to display it in the process interface, to do this:
Go to interface settings of the stage, where you want to display the created field. Select the universal block, where this additional field will be displayed:
Check the box next to the created additional field and save the settings:
After that this additional field will become added to the process: