Features:

• Cross-platform support for Linux and Mac
• Automation (so there's no need to remember to click "backup")
• Point-in-time recovery (or something close) so if you accidentally delete a file but don't notice until later, it's still recoverable
• Low cost
• Replicated data store for backup sets, so data exists in more than one place (i.e., not just backing up to a local USB drive)
• Encryption in case the backup files fall into the wrong hands