We use the full Google Apps suite: e-mail, calendar, shared cloud storage, google docs & sheets, etc. I really like the functionality of it all and the collaboration it enables for our virtual team, though the usability of Google Drive is pretty painful for me, and I still use Excel over Google Sheets for many things. Still, I'm very pleased with the solution overall.
We also use Slack, which has almost entirely replaced internal e-mail for us, with something far more powerful - unlike e-mail, the total transparency means there's no lost "organizational memory" when roles change, on top of numerous other benefits. It's definitely required some habit changes to integrate, and not everyone loves it personally, but I love what it's doing for the business regardless - if I were starting another company, it'd be at the top of my list of the most important software to adopt immediately.
Of course, I've got to mention GlassFrog here as well: aside from holding all of our key governance data, we use Notes on roles & circles to give us a basic intranet / knowledge-management system. Some of those notes hold information directly, and others link to a Google Doc/Sheet or other files in Google Drive; one way or another, much of our important data is linked from GlassFrog, so they're all catalogued by role/circle and more easily findable.
For video collaboration, we mostly use BlueJeans (it's pretty good, though it does have some issues and it's expensive enough that I doubt it'd make sense for many organizations). One of our teams also uses Google Hangouts quite a bit.
Hope that helps!