What we use:

* Skype / Facetime for videoconferencing

* Misc. chat apps

* Dropbox / Google Drive for file sharing

* Some git repos on a VPS box for source control

* Google calendar for calendars

* pinboard.in for link sharing (not perfect, but does the job)

* trello for project / business management

* Google Docs - for pairing on writing documents

* CrashPlan - for backups

* Office 365 - for dealing with MS docs from other people. LibreOffice just doesn't seem to cut it enough unfortunately when it comes to document exchange.