Clearspace ships with a simple approval workflow system. You are allowed to select people that should approve a document. The approvers can be forced on all documents at the space level that are created, or can be added by authors at the invidual document level. Though this system is quite powerful and sufficient for many circumstances it may not fit everyone's needs. This is why we built workflow on Open Symphony's OSWorkflow architecture.
OSWorkflow allows entire new workflow processes to be added to Clearspace. Clients can define and customize the workflow system by changing an xml configuration rather than rewriting parts of the core document api.
Customized workflows can be written via a Clearspace plugin. The plugin will contain custom workflow classes, the workflow configuration, and any additional workflow related webwork actions and pages. Your workflow can then be deployed at runtime without having to redeploy the core Clearspace application.