OwnCloud
ownCloud is software for file hosting, synchronization, file sharing and collaborative document editing.
The ownCloud user manual can be found here.
You can download the desktop synchronization app here. Apps for iOS and Android are available here.
You can access your ownCloud via the web interface as well, at https://cloud.yourdomain.com/owncloud.
Your ownCloud files are also available in the webmail interface (Roundcube), where you can add them as attachments to emails. For this to work, it is recommended to keep the password of your owncloud account the same as your email account.