This small distro is incredibly fast and effective, we use it for SMB with AD authentication, around 300 clients, and to provide a few large LUNs to ESXi. The performance is way better than commercial products, just set it up and you'll forget it's there
PetaSAN - PetaSAN is an open source Scale-Out SAN solution offering massive scalability and performance.
StorPool - StorPool is designed from the ground up to provide cloud builders, shared hosting providers and MSPs with the most resource efficient storage software on the market.
XigmaNAS - File Sharing, OS & Utilities, and Security & Privacy
VMware vSAN - VMware vSAN is radically simple, enterprise-class software-defined storage powering VMware hyper-converged infrastructure.
TrueNAS Core - TrueNAS Core (formerly FreeNAS) is a storage operating system strong and robust enough to meet the needs of enterprise level businesses.
DataCore SANsymphony - SANsymphony is a Software-Defined Storage powered by DataCore Parallel I/O technology for virtualization solution.