Hi!
I also feel that the requirements are slightly vague, but I get a feeling that you may want to take a look at RESTful web services and HATEOAS (
http://en.wikipedia.org/wiki/HATEOAS).
Here is a good article on how to implement workflows with RESTful web services:
http://www.infoq.com/articles/webber-rest-workflow
Frameworks that can do RESTful web services include
JBoss RESTEasy, Apache CXF, Jersey (JAX-RS reference implementation) and Restlet.
Please do not hesitate to ask if there are additional questions!
Best wishes!