Zentyal (formerly eBox Platform) is a small business server that offers small and medium businesses an affordable and easy-to-use enterprise-level computer network. It can act as a Gateway, Infrastructure Manager, Unified Threat Manager, Office Server, Unified Communication Server, or a combination of these.
Resara Server is an Active Directory compatible open source server for small businesses designed around Samba 4. It is designed to be simple and easy to use. Setup only takes a few minutes. The management console lets you manage users, share files, work with storage, and configure DHCP and DNS.