ubun2^beta

I am looking for a good free ubuntu backup software tool, please help.
 
Please suggest the best free open source and not commercial software you have used for quite some time and happy about it.
 
It would be great if the software has the following features

• Backup folders
• Restore folders
• Differential backup
• Scheduled backup and restore
• Backup while the machine is idle
• Support multiple hardware like USB, External Hard Drive, etc.,