The following is a list of the current recommendations for Open Source software in various categories. At the present, none of these items are sponsored - we are not receiving any financial support for mentioning any companies on this page.

Operating Systems

• CentOS Linux - Community Enterprise Linux, supported by the community and based on the Red Hat Linux code-base. Stable, reliable, and with long product life-cycle, this platform can be used consistently for many years.
• OpenSuSE Linux - If you need the latest, cutting-edge features, OpenSuSE is a fantastic distribution with a very short lifecycle and active development. It provides the basis for the SuSE Enterprise Linux platform, with a strong community and lots of extra add-ons.
• Red Hat Enterprise Linux - Requires a subscription for support and updates, but a good choice if you need the long lifecycle and commercial enterprise support. Red Hat is a recognized leader in the Open Source community and in bringing Linux to the enterprise.
• SuSE Linux Enterprise - SuSE Linux Enterprise Server (SLES) and SuSE Linux Enterprise Desktop (SLED) are recognized leaders in the Enterprise Linux space, with solid commercial support, regular updates, and long product life-cycles. SLES is also a recognized leader in non-Intel platform support for those who want to run Linux on platforms like IBM's Power series.
• Ubuntu Linux - Another Linux distribution with good support backing and long-term support, Ubuntu is a platform recognized for both its community availability and support as well as good options for commercial enterprise support.
• FreeBSD - For situations where you need a BSD platform instead of a Linux platform, FreeBSD is the recognized leader in BSD-style operating systems. With wide community, platform, and application support, it is a leader in the O/S space for server-side applications.

Virtualization

• Xen - Xen is the original and best hypervisor on the market. It is bundled in a variety of different forms, the most popular of which is likely the Citrix XenServer product.
• oVirt - Based on the KVM hypervisor, this is the open source base for the Red Hat Virtualization (RHV) product. It sports a number of different features, including a web-based management interface and automated installation for virtualization nodes.

Storage

• OpenZFS - There are number of different open source implementations of this amazing filesystem, including ZFS on Linux and FreeBSD's ZFS driver. Implementations also exist for Illumos (OpenIndiana) and Mac OSX.
• GlusterFS - A scalable, distributed network file system, and one of the most capable and popular software defined storage systems on the market today.
• Ceph - Another distributed network storage system, this one very object-oriented.
• Linux I/O - This is a target SCSI framework that supports a wide variety of SCSI-compatible targets, including FC, FCoE, iSCSI, and SCSI.

Databases

• PostgreSQL - Although it gets less press than MySQL and MariaDB, PostgreSQL is the leader in enterprise-level open source database. PostgreSQL conforms to SQL standards and has a wide variety of support for various languages and middleware, including C/C++, Java, Perl, PHP, and Python, and runs on a wide variety of platforms, including Linux, Windows, FreeBSD, and Solaris. PostgreSQL is used in many appliances, including Cisco's UC and Telepresence platform.
• MariaDB - Forked from the MySQL code-base after the acquisition by Oracle, MariaDB is a strong successor to MySQL and one of the recognized leaders in the Open Source database space.
• SQLite - SQLite is an alternative to full-blown RDBMS solutions, with strong support across multiple platforms and languages.
• MongoDB - If you need an object-oriented DB (OODB) instead of a more traditional RDBMS, Mongo is the recognized leader in the open source OODB space.

Middleware

• Apache HTTPD - One of the most popular and widely-used web servers on the market today, the Apache HTTPD product is powerful, configurable, scalable, and secure. It performs well, and has many add-on modules for extending functionality to various server-side languages, applications, and authentication schemes.
• Apache Tomcat - Tomcat is the most widely-used middleware platform, a recognized leader in Java-based application middleware. It has strong integrations with other products via Java-based connectors and is a stable, reliable, and secure middleware platform.
• JBOSS - The JBOSS platform, a Red Hat product, is another very widely-used Java-based middleware platform. It has both community and commercial support options, and runs on a wide variety of platforms and supports many application deployment types. JBOSS is used by many software producers as an integrated middleware platform for their applications.
• Nginx - For a lighter-weight web platform, Nginx is a very powerful, highly-configurable, secure and stable web server. While it lacks some integrations with other products and others are more difficult, it is widely used as a front-end proxy and load-balancer for other back-end servers and middleware platforms.
• Lighttpd - For the ultimate in light-weight web serving, lighttpd is available as a very basic web server and proxy. It has a small number of server-side applications that it supports, but is designed for ease of configuration and performance.

Appliances

• FreeNAS - An open source NAS distribution based on FreeBSD and ZFS. FreeNAS provides a wide variety of services for accessing storage, both NAS and block-based, and bundles it into a very clean, rich interface.
• Xen Orchestra - A management appliance for the Citrix XenServer platform. It comes in a few different editions, including both free/open source and enterprise/Supported.