ownCloud is open source software, built by a vibrant community of people like you!

dvcs-autosync is a project to create an open source replacement for Dropbox/Wuala/Box.net/etc. based on distributed version control systems (DVCS). It offers nearly instantaneous mutual updates when a file is added or changed on one side but with the added benefit of (local, distributed) versioning and that it does not rely on a centralized service provider, but can be used with any DVCS hosting option including a completely separate server - your data remains your own.

SparkleShare is a collaboration and sharing tool that is designed to keep things simple and to stay out of your way.

Syncany is an open-source cloud storage and filesharing application. It allows users to backup and share certain folders of their workstations using any kind of storage, e.g. FTP, Amazon S3 or Google Storage.