When you are orchestrating business processes in the organization, what you are controlling is the flow of information. This information can be used for taking decisions using business rules, creating documents, etc. In some time of the process, generally at then, the information needs to be persisted in some sort of system for later consultation and reporting.
Procx provide this capability using industry standard Web Services. Inside processes, you can place web services activities and send information from forms through them. This allows you integrate with third party systems like accountant systems or customer relationship management systems. 
In a expense approval process for example, at the end you may want to send this information to the accounts payable system directly. Even more, if your third party application supports it, you can print the check also. Possibilities are endless.
Not only you can send information, but you can also receive information inside processes using Procx. You can use this for example for taking decisions. In a loan application, during the process you may want to check the credit score of the applicant, and make decisions based on that.
When talking about integration, web services are the best technology tool to use. They are easy to build by developers and almost any new software application is coming with pre-built web services for integration purposes.