If you're willing to try something a little different, there's the ICE platform from ZeroC. It's open source, and is supported on pretty much every OS you can think of, as well as having language support for C++, C#, Java, Ruby, Python and PHP. Finally, it's very easy to drive (the language mappings are tailored to fit naturally into each language). It's also fast and efficient. There's even a cut-down version for devices.