Within Teamwork Projects, there are two types of user licenses: standard users & collaborators.

When inviting a new user to your site you can choose to add them as a standard user or collaborator.

The idea behind adding a collaborator is that you can bring your clients into your projects without incurring extra costs.

They can perform basic actions such as completing tasks assigned to them, milestones assigned to them, edit files they upload, add & reply to messages, add comments, and set privacy on project items.

Collaborators cannot add new tasks, task lists, milestones, notebooks, links, log time, view the calendar or set statuses. 

You can choose between these by selecting the drop down option next to the company you have chosen for them:

When a standard user is added, they can be given full permissions right up to administrator level and each standard user is counted in your recurring bill.

If you have chosen collaborator, they will have limited permissions but are completely free.

You can also change an existing user to a collaborator by navigating to the people section of your site.

To the far right of the user you wish to change you can choose the pencil icon and then select the Essentials tab. You can then update the type to standard or collaborator:

Note: When viewing the people section. Users will appear in green, contacts will appear in blue and collaborators will appear in pink:

When a user is set as a collaborator a message will appear within their permissions screen notifying you that they will have reduced permissions:

For more information, see: Understanding user permissions and access