NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
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ClearOS - A very good alternative for Windows Server, for free
Leadiro - Seriously Smart & Live B2B Data
Univention Corporate Server - Univention Corporate Server UCS with Active Directory functions and App Center is the cost-efficient and popular successor to Microsoft's server solutions.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.