ChucK is a new audio programming language for real-time synthesis, composition, and performance, which runs on MacOS X, Windows, and Linux. ChucK presents a new time-based concurrent programming model, which supports a more precise and fundamental level of expressiveness, as well as multiple, simultaneous, dynamic control rates, a precise and straightforward concurrent programming model, and the ability to add, remove, and modify code, on-the-fly, while the program is running, without stopping or restarting. It offers composers, researchers, and performers a powerful and flexible programming tool for building and experimenting with complex audio synthesis programs, and real-time interactive control.

What you need (to build your own):

• source
• dependency: libsndfile
• ALSA, JACK, or OSS
• gcc, lex, yacc, make

Full instructions can be obtained from the developer's website. Executable also available via download link.