For a workflow engine on the cloud you need following modules:
SharePoint Developer Daschboard (can be activated with STSADM.EXE)
BizTalk for Integration of Services
SharePoint for Human Interaction
AppFabric for Business Process Integration
SharePoint Explorer (available on CodePlex to show a Directory and Folder structure View)
BizTalk Feature Pack with Extensions for AppFabric Endpoint in the cloud; works like a Reverse Proxy.