StableBit DrivePool - State of the art, file based drive pooling software.
XigmaNAS - File Sharing, OS & Utilities, and Security & Privacy
btrfs - Btrfs is a modern copy on write (CoW) filesystem for Linux aimed at implementing advanced features...
Amahi - Amahi is a media, home and app server software known for its easy-to-use user interface. Amahi has the best media, backup and web apps for small networks.
mhddfs - The driver combines a several mount points into the single one.
PetaSAN - PetaSAN is an open source Scale-Out SAN solution offering massive scalability and performance.