Tools for complex collaborations

When we collaborate on a writing or editing project with one or two people, we can get away with sharing documents as email attachments. In more complex projects, we might have multiple partners, and each partner could have a significant amount of research and/or writing to contribute. Collaborative partners might have their own teams or student assistants who contribute to the effort. Sharing attachments is no longer the best strategy for exchanging work in progress, so what should we do?