gotcha. thanks. silly me to search for "license" and forget "copyright". while not a "typical OSS license", the copyright is clearly violated if Rybka is a derivative, since it's a commercial app and has been entered into competitions. thanks for pointing me to the copyright.

Where's the license for Crafty? I checked the website and the source code, and i can't find the word "license" anywhere at all... It's still unethical to use someone else's code without giving them credit, but I am not sure if he has violated the license if the license itself cannot be found.

Full disclosure - I am a founder of a startup that develops an open source automated trading platform targeted at institutional investors.

As was mentioned in above postings, there are a series of open source tools available to bootstrap your trading system development:

• QuickFIX and QuickFIX/J (I'm also a developer of QFJ project) - a C++ and Java open source implementations of the FIX protocol, the underlying standard protocol for connectivity between financial institutions. Think of it as the HTTP of finance.
• QuantLib - an open source risk analytics package
• Esper - an open source complex event processing engine
• EclipseTrader - Eclipse-based open source trading GUI that's targeted more at retail investors
• ActiveMQ and AMQP and Qpid for messaging (AMQP standard was initially contributed by JPMorgan)

And then of course there's my company Marketcetera - we build on top of a lot of the tools mentioned above and others (ActiveMQ, MySQL, Ruby on Rails, QFJ, etc) to provide the basic underlying platform that institutional traders (think quantitative hedge funds) can use to build their proprietary algorithms and start trading. After implementing a few trading systems in a row ourselves for various trading firms we realized that there was an obvious need for an open source trading platform so that people wouldn't have to reinvent the wheel and write systems from scratch every single time.

To answer the OP's question about which commercial firms use FOSS: - a lot of proprietary trading software is implemented on top of OSS - JPMorgan famously built their trading GUI [PDF] on top of Eclipse, and Progress Apama is built on top of Eclipse RCP as well.

Not surprisingly, most trading applications are very Windows-heavy (although quite a few companies have Linux clusters, and some exchanges run on Linux as well). Most of the apps that your broker will provide for you to trade with are Windows-only (such as Bloomberg, Goldman Redi, MicroHedge, etc), and a lot of the APIs available from vendors are .NET or COM components and nothing else. We implement our systems mostly in Java (including the Eclipse RCP), thought have connectors for some of the Windows-specific components.

We know that flexibility is at the heart of any powerful trading application, and we think the open-source model maximizes the ability of our users to control the application. Some think the open-source model is antithetical to the secretive finance industry, but we see it as the perfect fit.