Yes, drive rails. These are actually useful and not a hindrance. Many people were turned off from using drive rails years ago by companies such as Packard Bell. Unlike with those computers, all the rails you will ever need for the case are included. Rails provide an easy way to quickly remove drives from your case.
Posts slide into the normal screw holes on the drive.
Then just slide the drive in as you normally would. The posts and rails provide a surprisingly snug hold on the drive. You can really build a system quickly with these things. The internal drive bays are part of a removable drive cage. The cage itself slides in and out of the case, so you can easily add or change hard drives.