There are significant differences between a business rules engine and a workflow engine. A workflow engine can automate end-to-end, multi-layered processes of various complexities and timing, where a rules engine simply evaluates expressions and decision criteria. Both engines are designed to be used by technical and non-technical people alike. A workflow engine manages integration and automation comprehensively and makes use of rules through a business process analyst. A business rules engine analyzes and processes rules - rule that can be simple to complex, cascading, or even dynamically generated. But, at the end of the day, rules engines are limited to processing rules.
Earlier this year, Gartner put out an article talking about how Rules Engine within Workflow/BPM process automation. We all know in today's landscape of tasks, assignments, workflow/sub-workflows, the need for automating business processes is greater than ever.