The ownCloud project was created to allow easy maintenance of your own private server providing common "cloud" type services. Features include:
Current features: file management, WebDAV access, share via public link, music streaming, users & groups, OpenID, LDAP
In development: sharing, encryption, calendar, contacts, etc., desktop sync client, Android & webOS apps, server-server sync
Planned: file editing, versioning & recovery, connecting to other services
It is available in Ubuntu repositories as the
owncloud package, though since it is under such active development that version is now slightly outdated - instructions to install the latest version can be found in the Administrators Manual.
There is also a blog, and a Q&A site similar to AskUbuntu.