Google Drive is great for sharing and collaborating on files and documents.
Slack is great for discussions, with separate chat channels and group/private messaging. They have really good apps for iOS, Android, and Windows. It also bridged the mentor and student communication in a way not possible on social media. Great for file sharing, it also features convenient integrations with apps like Google Drive, Twitter, and Git.
Slack and Google Drive comprised Team 1257’s new and improved communication system last year, and I couldn’t be happier with how well it worked.