Complex sentence: "Add-Ons" are separately priced additional backup server features, for example to protect open NTFS files on Windows systems or Advanced Tape Support, for backing up to multiple single tape drives simultaneously or to a multiple-drive tape library.
Split into simpler sentences: Add-Ons are separately priced additional backup server features. Another Add-On is Advanced Tape Support, for backing up to multiple single tape drives simultaneously or to a multiple-drive tape library.