FlowDesigner

FlowDesigner is a free (GPL/LGPL) data flow oriented development environment. It can be used to build complex applications by combining small, reusable building blocks.

In some ways, it is similar to both Simulink and LabView, but is hardly a clone of either. FlowDesigner features a RAD GUI with a visual debugger. Although FlowDesigner can be used as a rapid prototyping tool, it can still be used for building real-time applications such as audio effects processing.