Windows Small Business Server Linux Alternatives

http://www.ebox-platform.com/
eBox Platform

eBox Platform is an open source small business server that can act as a Gateway, a Unified Threat Manager, an Office Server, an Infrastructure Manager, a Unified Communications Server or a combination of them. All network services are based on the same technology and fully integrated, allowing you to manage your network easily as a one single unit!
eBox 1.2 Feature list ¶

* Networking
o Firewall and routing
+ Filtering
+ NAT and port redirections
+ VLAN 802.1Q
+ Multi-gateway support, load balancing and automatic failover
+ Traffic shaping (with application layer support)
+ Graphical traffic rate monitoring
+ Network intrusion detection system
+ Dynamic DNS client
o Network infraestructure
+ DHCP server
+ NTP server
+ DNS server
o VPN support
+ Dynamic routes autoconfiguration
o HTTP proxy
+ Internet cache
+ User authentication
+ Content filtering (with categorized lists)
+ Transparent antivirus
o Intrusion Detection System
o Mail Server
+ Virtual domains
+ POP3 and IMAP with SSL/TLS
+ Spam and antivirus filtering
# Greylisting, blacklisting, whitelisting
+ Transparent POP3 proxy filter
o Web server
+ Virtual hosts
o Certification authority

* Workgroup
o Centralized users and groups management
+ Windows PDC support
o Network resource sharing
+ File server
# Antivirus
+ Print server
o Groupware: calendar, address book, webmail, wiki, etc.
o VoIP server
+ Voicemail
+ Conference rooms
+ Calls through an external provider
o Jabber/XMMP server
+ Conference rooms
o eBox User Corner for self users info updating

* Reporting and monitoring
o Dashboard for centralized service information
o Monitor CPU, load, disk space, thermal, memory
o Disk usage and RAID status
o Summarized and full system reports
o Event notification via mail, RSS or Jabber

http://www.howtoforge.com/using-ebox-as-windows-primary-domain-controller

Using eBox As Windows Primary Domain Controller

eBox Platform is an open source small business server that allows you to manage all your services like firewall, DHCP, DNS, VPN, proxy, IDS, mail, file and printer sharing, VoIP, IM and much more. These functionalities are tightly integrated, automating most tasks, avoiding mistakes and saving time for system administrators.

This tutorial shows you step by step how to use eBox as Windows Primary Domain Controller. At the end of it you will be using eBox Platform 1.2 for users and shared resources management on your Windows domain.

http://www.clearfoundation.com/Software/introduction.html

ClearOS is a powerful network and gateway server designed for the small business and distributed environments. Though ClearOS comes with an extensive list of features and integrated services, the solution is easy to configure thanks to the intuitive web-based interface.

The open source revolution in the software industry has made it possible to provide ClearOS at no cost. Among other features, antivirus, antispam, VPN and content filtering are built right into the software -- no need for expensive third party add-ons. Before making a decision on whether to subscribe to ClearSDN services and updates for ClearCenter, you can take advantage of the free ClearOS download at any time. One of the most important tasks when deploying server systems is the ongoing monitoring and maintenance. ClearSDN offers a suite of Gateway and DNS services to make sure your system is up-to-date, secure and running smoothly. As an open source distribution, you can download ClearOS and receive free security updates for 18 months. Download, test, play, turn features off, set it up for anything you like - all for free. There are detailed instructions here and tons of help in the forums. If you want more help, we'll set you up quickly with a ClearCenter partner that fits your needs. Thank you in advance for using ClearOS and have fun!

* ClearOS, Microsoft, Cisco, Barracuda, Oracle and Sonicwall are either pending or registered trademarks of their respective Corporations.
ClearOS Modules

* Advanced Firewall Module
* AntiSPAM Module
* AntiSPAM Quarantine Module
* Antivirus Module
* Bandwidth Manager & Limiter Module
* Caching Name Server Module
* Content Filtering Module
* Directory Services Module
* Firewall - DMZ & 1-to-1 NAT Module
* Firewall - Gateway Module
* Firewall - Peer-To-Peer Module
* Flexshare Centralized Storage Module
* FTP/S Server Module
* IPSec VPN Module
* Mail Drop Module
* Mail - IMAP/POP Server Module

* Multi-WAN Module
* MySQL Database Server Module
* Network Toolkit Module
* Network Tools & Configuration Module
* OpenVPN Module
* PHP Module
* PPP Module
* PPTP VPN Server Module
* Print Server Module
* SSL Certificates Module
* Status Information Module
* System Statistics Module
* Web Access Module
* Web Log File Analyzer Module
* Web Proxy Server Module
* Web Server Module
* Windows Networks & File Sharing Module
* Software Modules | Security & Bug Fix Updates (No Upgrades)
* Remote Config Backup (Optional)
* AD Web Authentication Module* and many more on the ClearOS | Road Map