Drools!

Joget Workflow is an open source web-based workflow software to develop workflow and Business Process Management applications. More than just a workflow or BPM platform, Joget offers full-fledged agile development capabilities (consisting of processes, forms, lists, CRUD and UI), not just back-end EAI/orchestration/integration or the task-based interface for traditional workflow/BPM products. So for example, build a CRM sales force automation app instead of just a sales quotation approval process. »

Build Python/Django process-driven workflow web apps for browsers or mobile devices. Start with loads of pre-built rules, or author your own rules in pure Python.

Ruote is a workflow engine written in Ruby. Ruote is not a state machine library. Ruote as a workflow engine comes as an “onion”. There’s a storage at the core, taking care of all the persistence. A worker where all the orchestration work happens surrounds the core. The dashboard has all the levers to launch, pause, cancel process instances.

Automate and govern repeatable decisions.

Download NxBRE. NxBRE is a lightweight Business Rule Engine (aka Rule Based Engine) for the .NET platform, composed of a forward-chaining inference engine and an XML-drive

SRE (Simple Rule Engine) is a lightweight forward chaining inference rule engine for .NET. Its 'simple' because of the simplicity in writing and understanding the rules written in XML, but this 'simple' engine can solve complex problems.