Share/Duplicate posts with fellow multisite user

I have a user driven WP multisite that let’s my college students create their own portfolio sites. http://spadelhi.org/

I want the users (students) to be able to share/copy/duplicate some posts (projects) with fellow users (by linking to their email id or selecting from the userlist) such that multiple users can share/have the same project (display it in their portfolio).

How can I achieve this? Some plugin?

PS- I hope I made some sense there. 😀
Sample Portfolio – http://spadelhi.org/spartandemo