Can I customize the workflow so it can call agents/scripts/applets that I write?
Sure. Of course.
A workflow tool that won't let you easily incorporate custom code isn't much of a workflow tool.
The need to run custom code, whether to access outside data sources, check for the completion of related documents, set hide-when flags, or for any of a hundred other purposes is simply something you have to be able to do when building sophisticated workflows.
Of course you can run custom code with ProcessIt!
If you can do it in Lotus Notes or Domino, you can do it with ProcessIt!
Smart people building sophisticated applications & workflow tools for Lotus Notes, IBM Lotus WebSphere and the Internet