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.
Collax Groupware Suite is a complete collaboration, e-mail, and messaging server with Outlook MAPI support. It offers enterprise email server functions, anti-spam and anti-virus filters, GUI management, a file server for SMB, NFS, FTP, and Apple shares, backup/restore server, IM server, and fax and SMS server. The groupware offers AJAX Web mail, calendar, team calendar, contacts, and tasks, and supports ActiveSync for mobile devices. It is free for private or commercial use of up to five users.