There are a few paths that you can take for your open-source SOA initiative. You can go with a complete open-source SOA stack, you can mix and match various open-source SOA products from different vendors, or you can mix and match both commercial and open-source products.

There are two major open source stack providers that stand out: MuleSource and WSO2.

Mulesource

MuleSource launched the Mule ESB back in 2003. In 2006, they formed an actual company and continued enhancing their product offerings. In addition to the ESB, they have an application and services monitoring tool called MuleHQ, and a design-time governance tool (just released) called MuleGalaxy.

To complete their stack offering, MuleSource works with open-source partners Liferay for portal functionality and Intalio for BPM functionality. Do you need proof that Mulesource is ready for prime time? Just ask H&R Block, which has a 130,000 server Mule ESB implementation [PDF] or read about Walmart.com [PDF].

WSO2

WSO2 is a true open-source alternative. Unlike many open-source vendors in this space, they do not have a separate commercial and enterprise offering. All of their features are free, with the hope that their customers will acknowledge the need to purchase subscription services. This is a great strategy because it allows the customers to see the full value of the products without having to deal with the limitations of a community version. WSO2 is three years old and started with a Web Services Framework, which is a communication run time that they offer for Perl, PHP, Ruby, Spring, C and C++.

Web Services Framework is a set of libraries and jar files for rapid development and deployment of Web services. On top of this framework, WSO2 is building its SOA offerings which include an ESB, Web Services Application Server, a runtime governance tool, a security solution, and a newly released mashup server. The Web Services Application Server makes it simple and effective to create, consume and manage Web services' it provides data services capabilities and will soon include a rules engine. The new Mashup Server makes it easy to compose Web services, feeds and Web pages to create mashups through the use of a simple scripting language.

Do you need WSO2 case studies? Some of their customers include a large HMO with a legacy mainframe system that is using WSO2's Data Services and ESB, Concur (a Web 2.0 Expense Management company that is using their Data Services and ESB to implement an internal SOA) and one of the largest banks in the AsiaPac area, getting support for their ESB.