Blackboard provides tools that can be used to help promote collaboration between students.
Wikis
Wikis allow students to create multiple pages that can be linked together, to form a simple website structure. Text and media elements can be inserted on each page. Project teams are able to create and edit the text within each page. Every wiki has a rollback (history) functionality, to track and reverse changes. Combine a wiki with a discussion forum to allow prior discussion of page edits.
Blogs
Blogs can be used to create peer-supported communities. The ability to allow comments from readers moves a simple blog post to a much more discursive learning experience. They can also be used for practical uses such as recording tasks that have been completed within a project.
Groups
Groups allow a cohort of students to be divided up for many purposes, often to work collaboratively.
All of the above tools can be deployed on a group by group basis to further enhance the collaborative working experience.