PetaSAN - PetaSAN is an open source Scale-Out SAN solution offering massive scalability and performance.
StableBit DrivePool - State of the art, file based drive pooling software.
XigmaNAS - File Sharing, OS & Utilities, and Security & Privacy
Greyhole - Greyhole is an application that uses Samba to create a storage pool of all your available hard drives, and allows you to create redundant copies of the files you store, in order to prevent data loss when part of your hardware fails.
Dell EMC UnityVSA - dell-emc-unityvsa-overview-deployment
mhddfs - The driver combines a several mount points into the single one.