What programming language would you use if you wanted to write some server code that needs to run on Windows, Mac OSX, and Linux?
Specifically, the software runs as a server. Ideally it will be able to run the same codebase a) on the desktop for a single user , b) on an intranet server for multiple users, and c) on an internet server farm for millions of users. While that sounds like an overly ambitious requirement, it may actually be realistic with proper consideration up front.
There will also need to be a lightweight client-side user interface for the desktop scenarios. The simple frontends could be coded on a platform-by-platform basis, but if anyone has recommendations for cross-platforms UI toolkits, I'd love to hear that too.
Ideas?