Following my post about amatea, Egon has suggested me to have a look at two softwares:
KNIME is a modular data exploration platform based on Eclipse that enables the user to visually create pipelines, selectively execute some or all analysis steps, and later investigate the results through interactive views on data and models.
NIME offers the possibility to extend its functionallity by creating your own nodes.
The Taverna project aims to provide a language and software tools to facilitate easy use of workflow and distributed compute technology within the eScience community. At first glance, it works with web services, but I need to investigate a little more about it.