You can share a project with external collaborators in read only mode, at any time such collaboration can be terminated.

In order for this option to be available to the users, the account owner should allow this in the account settings page

1. To set and manage your collaborators, go to the project show page, More menu > Share project:

2. When the account owner, admin or the project owner clicks on share project a new pop-up window will be opened to set up the external collaborators:

Here you can fill the name and email of the collaborators (required fields), then click on "send link".
​
3. The invited collaborators will get the following email: 
​

They will be able to use the link to access this project in read-only mode.

The owner of the project, admins and the account can view and manage the collaborator list of a specific project with the option to stop sharing if needed:

The owner of the project and account admin, can view the collaborator list of an specific project.

After clicking on stop collaboration, the collaborator won't be able to view the project content anymore:

Additionally, you can find the 'Collaborators' tab under the account settings menu. The account owner and admins can see and manage the list of all the collaborators they are working with, on which project, and the option to stop the collaboration as described above.