Linux tends to take center stage when it comes to support and other services for enterprise open source users. However, there are literally thousands of other solid open source packages available that perform a wide variety of functions. Unfortunately, there's a real lack of information about the options and considerations for selecting open source that not only meets the functional and technical requirements of specific tasks, but has the support and backing that enterprises need to manage risk. As a result, with enterprise developers lost in a sea of open source options, it can be a daunting task to make the best choice.

Highlighted below are 10 popular open source projects that enterprises can look to when considering open source alternatives in their IT infrastructure. I've highlighted a few key open source components in some of the most asked-for categories - Web Services, Service Oriented Architecture (SOA), Integration, Frameworks, and Libraries. Each project selected has at least one vendor offering commercial support. At the end of this article, I'll offer a basic checklist for those who are evaluating open source to ensure that the open source software they select fills all of their technical and business-related needs while managing corporate risk.

Web Services
XFire
XFire is a Web Services framework (hosted by Codehaus) that allows developers to create and/or consume Web Services. Given its simplicity of use and built-in testing tools, it makes short work of Web Services by effectively eliminating the manual labor of generating WSDL and other artifacts of SOAP. XFire is compatible with a variety of commercial and open source Web Services frameworks, including Apache Axis and Microsoft Web Services.

Major pros of this relatively new project are that it's up-to-date, fast, built to integrate with other frameworks like ServiceMix, and supports JAX-WS - an easy-to-understand architecture for Web Services development that can be used to build Web applications and Web Services with newer XML-based functionality.

However, because XFire is so new, many organizations have already become comfortable using Apache Axis - the original open source Web Services offering. Companies might feel more comfortable choosing Axis over XFire simply because of name recognition.

The license for Xfire isn't an OSI-approved license but it is very liberal, only requiring a copyright notice. Xfire is in the process of merging with Celtix, backed by Iona Technologies. Envoi Solutions and OpenLogic offer commercial support.

Axis2
Similar in function to XFire, Axis2 is a core engine for Web Services. Like XFire, Axis2 supports SOAP and other standards, but it also has integrated support for the Representational State Transfer (REST) style of Web Services. Axis2 is a more efficient, modular, faster, and more XML-oriented (it has the new fast AXIOM XML parser) solution than the original version. It supports plug-in modules that extend functionality for features such as security and reliability, factors critical to enterprise IT.

The primary downside of Axis2 is that it's plagued by the stigma of the first Axis, which has the reputation of being poorly documented and difficult to use. However, Axis2 does offer more documentation, which is a marked improvement over the earlier version.

Axis2 is an Apache Software Foundation project and is available under the Apache 2.0 license. Commercial support is available from several companies including Covalent, OpenLogic, and WSO2.

Choosing between Axis2 and XFire really comes down to what you need to plug into. XFire is meant to be easily pluggable and work with a slew of other frameworks, including ServiceMix, while Axis2 is better suited for standalone use, although it's also pluggable if necessary. These two offer less expensive open source alternatives to proprietary Web Services solutions like those offered by Microsoft. Unless companies are using a full-blown SOA implementation where they get everything from a vendor (BEA, for example), they would probably want to opt for an open source solution like these two for reasons of cost and simplicity.

SOA
ActiveMQ
ActiveMQ is the most popular and powerful open source Message Broker. Although not quite a full-blown SOA solution, its flexible messaging technology is required for any SOA implementation. Widely considered one of the best Java Messaging Service (JMS) implementations available, ActiveMQ is fast, pluggable, and easy to embed into homegrown software, especially Spring-based applications. It's easily manageable through JMX, and it works with Apache Axis2 and XFire as well as servers like JBoss, WebLogic, and Geronimo. It also supports REST, many cross-language clients and protocols, including Java, C, C++, Perl, PHP, Ruby, and Python, and a wide variety of transport protocols. Regarding functionality, ActiveMQ provides a number of advanced messaging services offered by commercial vendors, such as Message Groups, Virtual Destinations, Wildcards, and Composite Destinations.

The drawback with ActiveMQ is that it's still fairly young and evolving, so it might require heavier configuration rework than enterprise developers want to accept. Although this extreme configurability is a major asset of ActiveMQ, it requires time to configure correctly for your circumstances.

ActiveMQ is an Apache Software Foundation project and available under the Apache 2.0 license. Commercial support is available from LogicBlaze and OpenLogic.

ServiceMix
This project provides an Enterprise Service Bus (ESB) that combines the functionality of a Service Oriented Architecture (SOA) and an Event Driven Architecture (EDA) to create an agile enterprise ESB. It's built on Java Business Integration (JBI) and supports BPEL in conjunction with rules engines. It has dozens of transports and plug-ins and is lightweight, easily embeddable, and offers integrated Spring support. It works standalone or within Geronimo or JBoss and sits on top of ActiveMQ. It has e-mail integration, Web Service integration, virtual file system integration, XSLT transformation, content-based routing, and Groovy support for end-point scripting.

ServiceMix is the most configurable and adaptable open source ESB implementation available. Like ActiveMQ, though, ServiceMix's configurability is a blessing and a bane. The project is still young, and it will go through many iterations and require a lot of configuration by developers. Also these open source alternatives don't offer a lot of user interfaces for policy administration, management, control, flow design, or the other bells and whistles offered by commercial competitors like Sonic and BEA.

ServiceMix is an Apache Software Foundation project and is available under the Apache 2.0 license. Commercial support is available from LogicBlaze and OpenLogic.

Integration
POI
Java-based POI gives developers easy and direct access to Microsoft Office files, including Word and Excel. The documents can be parsed and generated, which makes it easy to create them on-the-fly for downloading purposes from a corporate Web site. So, if a developer needs to create a report that's required on the business end in Excel or Word, POI is the open source tool of choice.

Unfortunately, although it's top-notch for reading Word or Excel files, it currently can only create Excel files. The functionality to create Word files is reportedly in development.

POI is part of the Apache Software Foundation's Jakarta Project and is available under the Apache 2.0 license. Commercial support is available from OpenLogic.