Rclone is a command line program to sync files and directories to and from cloud storage services like Google Drive.

Dropbox like arrangement.

Conduit is a synchronization application for GNOME. It allows you to synchronize your files, photos, emails, contacts, notes, calendar data and any other type of personal information and synchronize that data with another computer, an online service, or even another electronic device.

Synchronize your Motorola RAZR V3 with Google Calendar

OpenSync is a PIM data synchronization framework that consists of several plug-ins that can be used to connect to different devices and systems.

MultiSync is a free modular program to synchronize calendars, addressbooks and other PIM data between programs on your computer and other computers, mobile devices, PDAs or cell phones.