According to a recent study by Stanford University consulting professor Jonathon Koomey, there are approximately 31.6 million servers installed around the world, including about 11.5 million in the United States. If organizations had to use only proprietary software for all of those systems, the resulting costs would be astronomical.
Fortunately, the open source community has a huge selection of server software that can lower those costs significantly. For this list, we focused on some of the top open source tools that offer alternatives to proprietary server software. We've organized them into categories to make browsing the list easier.
As always, if you'd like to suggest additional open source server software that you think should have been included on the list, please feel free to add it in the comments section below.
Content Management Systems
The "world's most popular open source CMS," Joomla runs 2.7 percent of the websites on the Internet, including sites for Harvard University, Citibank, IHOP and the Guggenheim Museum. It provides both a repository to manage your Web content and a platform to build your own Web applications. Operating System: OS Independent
Well-known users of this very popular CMS include the White House, the Economist, Fast Company and the World Wildlife Fund. It's highly flexible, robust and can be used for "everything from personal blogs to enterprise applications." Operating System: OS Independent
This award-winning Web content management system offers ease of use and a modular design. It's driven by a MySQL database and includes advanced user management features. Operating System: OS Independent
Alfresco combines document management, Web content management, records management and collaboration into a single package. In addition to the free community version, it also comes in paid Enterprise and Cloud versions. Operating System: Windows, Linux
Used by 700,000 websites, DotNetNuke claims to be "the leading open source Web content management system for ASP.NET." It comes in a free community edition and paid professional editions; in addition, more than 10,000 modules and skins are also available for purchase. Operating System: Windows
Downloaded more than 60,000 times, this CMS is growing in popularity, particularly among SMBs. As you might guess from the name, its claim to fame is its simplicity and intuitive interface. Operating System: Linux
Liferay includes content and document management, Web publishing, shared workspaces, collaboration, social networking and identity management capabilities. It advertises itself as simpler than WebSphere and more flexible than Sharepoint. It's also available in a commercially supported enterprise edition. Operating System: OS Independent
Boasting Fortune 500 and government users in more than 100 countries, Magnolia was designed to make it easy for business users to enter and edit Web content. Commercially supported versions are available with prices that vary based on the SLA. Operating System: Windows, Linux
WebGUI calls itself an "all-in-one CMS," and it offers both Web content management and a Web application development platform. In order to help users learn the software, the site offers a video tutorial and weekly training webinars. Operating System: Windows, Linux/Unix, OS X
Owl lets you create a knowledgebase or FAQ site. It's available in both a regular version and an "ultralite" version that does not use a database. Operating System: Windows, Linux
The "world's most popular open source database," Oracle-owned MySQL boasts high performance, high reliability and ease of use. In addition to the free community version, it's available in paid standard, enterprise and cluster carrier grade versions. Operating System: Windows, Linux, OS X
PostgreSQL calls itself "the world's most advanced open source database." Key features include Multi-Version Concurrency Control (MVCC), point-in-time recovery, online/hot backups, asynchronous replication, nested transactions (savepoints) and write ahead logging for fault tolerance. Operating System: Windows, Linux, OS X
Under development since 1981, Firebird is a mature RDBMS that boasts excellent concurrency, scalability and performance. Notable features include multi-generation architecture, high compatibility with ANSI SQL, logging and monitoring capabilities, online backup, full text search and more. Operating System: Windows, Linux, Unix, OS X, Solaris
Magento is the e-commerce platform of choice for more than 100,000 merchants, including Dockers, Ford, the North Face, Samsung, Oneida and others. In addition to the free community version, it also comes in paid professional and enterprise versions, and it's also available as a turn-key hosted solution for small businesses. Operating System: Windows, Linux, OS X
Award-winning PrestaShop is used by more than 95,000 Internet sites around the world. Commercial support and training are available, but prices are given in Euros. Operating System: Windows, Linux, OS X
Designed in part by ecommerce shop owners, Zen Cart is very user friendly, and the Web site offers simple instructions that begin with the basics: "Get a server." It includes features like multiple payment methods, multiple shipping options, a newsletter manager, coupons, quantity discounts and more. Operating System: OS Independent
Now owned by VMware, Zimbra offers a flexible but simple mail server with a low total cost of ownership. In addition to the free community version, it's also available in paid appliance and network editions, and a desktop e-mail client is available as well. Operating System: Linux, Unix, OS X
This turn-key mail server supports e-mail, group calendars, contacts, IM, a wiki and more, all accessible through a Web interface. It's also available on a hosted basis. Operating System: Linux
Estimates suggest that around 20 percent of all mail servers use Posftix, making it the most popular currently. Postfix was originally created by IBM Research as a better alternative to Sendmail, and it has also been known as "IBM Secure Mailer" and "VMailer." Operating System: Linux, Unix, OS X, Solaris
Although its popularity has declined in recent years, Sendmail still accounts for about 16 percent of the mail servers in use. Supported hard appliances and virtual appliances are also available under the brand name Sentrion. Operating System: Linux
Developed at the University of Cambridge, Exim is a highly configurable mail transport agent. It can handle thousands of e-mails per hour, but if queues are exceptionally large, it does not perform as well as some of the other options on the list. Operating System: Linux, Unix
FileZilla allows you to set up your own FTP server on a Windows machine. It supports FTP, FTPS and SFTP, and the same project also offers a cross-platform FTP client. Operating System: Windows
Now one of the most popular flavors of Linux, Ubuntu has a reputation for being easy to use and manage. It comes with built-in KVM virtualization capabilities, and it works with Ubuntu Enterprise Cloud to allow you to create a private cloud.
One of the most well-known enterprise distributions of Linux, Red Hat is known for its reliability, scalability and security. It includes integrated virtualization, the LAMP stack, the Eclipse IDE, and advanced management tools. Note that Red Hat requires a commercial support package.
Used by more than 13,000 businesses around the world, SUSE counts the London Stock Exchange, Office Depot, Sony and Walgreens among its high-profile users. In addition to the standard version, it also comes in System z, desktop, SAP, JeOS and other versions. As with Red Hat, SUSE requires commercial support; if you prefer an unsupported, free version, try openSUSE (below).
For those who don't want commercial support, the free openSUSE also comes in a server version. However, it does not have as many features and options as the commercial version.
Mandriva calls itself the "simple, high-performance, accessible Linux server." It provides Web, messaging, files, printing, virtualization and directory services. Note that the enterprise server version of Mandriva requires a fee.
When Oracle discontinued development of OpenSolaris, some of the developers who had been working on the project forked it to the Illumos project, where development and bug fixes continue. If you are looking for a free version of Solaris, this is the option for you. To download the software, visit the OpenIndiana page above.
Short for "Anti-Spam SMTP Proxy," ASSP stops spam at your mail server. Key features include easy browser-based setup, support for most mail servers, automatic whitelisting, virus scanning through ClamAV, Bayesian filters, community-based gray-listing and more. Operating System: OS Independent
This Linux distribution functions as both a network firewall and an application server. It also includes many open source network and sever monitoring tools. Operating System: Linux
This transparent proxy server works with Clam AV and other anti-virus software to scan incoming and outgoing e-mail for viruses, worms, trojans, spam and harmful attachments. Operating System: Linux
Small Business Server
With Zentyal, you get a gateway, an infrastructure manager, a unified threat manager, an office server and/ or a unified communication server all in one package. Professional support, training and add-ons are also available on the site. Operating System: Linux
Based on the CentOS distribution of Linux, SME offers file and print sharing, mail server, network firewall, remote access, a Web application server and more. It boasts thousands of users, good security and user-friendly setup and operation. Operating System: Linux
Server Log File Monitoring and Analysis
AWStats uses the log files from your Web, streaming, FTP or mail server to create easy-to-read graphical reports. It runs from the command line or as a CGI. Operating System: Windows, Linux, OS X
The self-proclaimed "most popular logfile analyzer in the world," Analog quickly generates usage statistics for Web servers. It can be used in conjunction with Report Magic to create more attractive graphs. Note that this project has not been updated in a while, but it is still used to analyze traffic on many servers. Operating System: Windows, Linux, OS X
Like AWStats and Analyzer, Webalyzer analyzes the statistics from Web servers. By default, it creates yearly and monthly usage reports which can be viewed from any browser. Operating System: Windows, Linux, OS X
The Snare project encompasses a number of different tools and agents, all of which assist in the filtering, collection and monitoring of server log files. Commercial support and the proprietary Snare Server are also available on the same site. Operating System: Windows, Linux, OS X, others
Based on BSD, this app allows you to create network attached storage for sharing files across Windows, OS X, Linux and Unix-like systems. Key features include a Web-based interface, the Zettabyte File System, snapshots, thin provisioning and more. Operating System: FreeBSD.
Very recently acquired by Red Hat, Gluster offers open source file systems for public and private cloud-based storage. Used with commodity hardware, the Gluster file system can create network storage solutions that scale out to 72 brontobytes. (The number of bytes in a brontobyte is a one followed by 27 zeros.) Operating System: Linux
Downloaded more than 250,000 times, Openfiler offers both file-based Network Attached Storage and block-based Storage Area Networking. Key features include volume-based partitioning, iSCSI (target and initiator), scheduled snapshots, resource quota, and a unified interface for share management. Operating System: Linux
Used by many commercial cloud services, the Xen hypervisor is included in most Linux distributions and is also available as an appliance. Many commercial virtualization products, including the Citrix XenServer, are built on top of Xen. Operating System: Windows, Linux, Solaris, others
VirtualBox offers virtualization for x86 and AMD64/Intel64 servers and desktops. Pre-built VirtualBox appliances are available for download from Oracle. Operating System: Windows, Linux, OS X, Solaris, others
OpenVZ takes a different approach to virtualization: unlike VMware, VirtualBox and many other virtualization solutions which use VMs, OpenVZ offers container-based virtualization through VEs or VPSs. Commercial products based on OpenVZ are sold as Parallels Virtuozzo Containers. Operating System: Linux
Short for "Kernel-based Virtual Machine," KVM allows users to run multiple Linux or Windows virtual machines on a single server. Like Xen, it's included in many Linux distributions. Operating System: Windows, Linux
Used by 63 percent of all websites, Apache has been the most popular Web server for more than a decade. It prides itself on being secure, efficient and extensible. Operating System: Windows, Linux, OS X
Nginx (pronounced "engine X") is both an HTTP and a mail proxy server. Currently powering about 8 percent of all websites, it's the third most popular Web server. Operating System: Windows, Linux, OS X
Often used alongside the Apache HTTP server, Tomcat offers a "pure Java" HTTP web server for running Java code. Well-known websites that use Tomcat include Walmart, E*Trade, The Weather Channel and many others. Operating System: Operating System: Windows, Linux, OS X
Most of them time when you want to install the Apache Web server, you'll also need other tools, like MySQL, PHP and Perl. This group of downloads bundles together all of those tools—along with a variety of other open source software that's helpful for running a Web server—in an easy-to-deploy package customized for each of the major operating systems. Operating System: Windows, Linux, OS X, Solaris
This is another project that bundles together Apache, MySQL and PHP into an easy-to-install package. However, this one only supports Windows. Operating System: Windows
The goal of the App Serv project is simple: allow users to set up a Web server with Apache, MySQL and PHP in one minute or less. Note that this project originated in Thailand so some of the English documentation reads a little strange. Operating System: Windows, Linux
If you just need a simple wiki, DokuWiki is easy-to-use, standards compliant and doesn't require a separate database. Commercial support is available through a variety of third-party companies. Operating System: OS Independent
Best known as Wikipedia's software, MediaWiki can handle extremely large projects with terabytes of data and thousands of hits per second. It's extremely customizable and is fairly simple for end users to learn. Operating System: Windows, Linux/Unix, OS X
Althought it's a little tough to find the open source version of MindTouch on the company's website, the source code for the core wiki program is still available for a free download. According to the website, it's been ranked the number one open source collaboration tool. The company offers several other products based on the open source engine. Operating System: Windows, Linux
More than just a wiki, TikiWiki also offers support for forums, blogs, image galleries, map servers, RSS feeds, bug trackers and more. It has been downloaded more than 900,000 times and currently powers tens of thousands of websites. Operating System: OS Independent