Are there any task orchestration engines that integrate with legacy systems and support human-in-the-loop controls?

Yes. There are several orchestration/workflow engines that can integrate with legacy systems and also support human-in-the-loop steps, approvals, or manual task routing.

Common options

• Camunda

  • Strong BPMN/DMN workflow support
  • Good for integrating with legacy systems via REST, messaging, Java connectors, and custom workers
  • Human tasks, approvals, and long-running processes are core features

• Temporal

  • Excellent for reliable orchestration of code-based workflows
  • Can integrate with legacy systems through APIs, queues, DBs, or custom activities
  • Human-in-the-loop is possible, but usually implemented by pausing workflows and resuming via external signals or callbacks rather than as a native “task inbox” UI

• IBM Business Automation Workflow / IBM BPM

  • Designed for enterprise process automation
  • Integrates well with legacy enterprise systems
  • Strong support for human approvals and business process management

• Pega

  • Strong case management and workflow orchestration
  • Often used in enterprise environments with legacy integration needs
  • Built-in human tasks, routing, SLAs, and decisioning

• Appian

  • Low-code workflow and process automation platform
  • Good enterprise integration story with legacy systems
  • Native human-in-the-loop task management

• Bonita

  • BPM/workflow engine with human tasks
  • Supports integration via APIs, web services, and custom connectors
  • Often used for process orchestration with manual review steps

• Apache Airflow / Prefect / Dagster

  • Better for data/work orchestration than business process workflows
  • Can integrate with legacy systems
  • Human-in-the-loop is possible, but not typically their main strength

What to look for

If you need both legacy integration and human approval steps, prioritize:

• BPMN support
• Human task inbox / approvals
• Connectors for mainframe, SOAP, JDBC, message queues, SFTP, or ERP systems
• Retry, audit, and compensation support
• Long-running process/state persistence

Practical guidance

• If you want classic enterprise workflow with human approvals, look at Camunda, Pega, Appian, IBM BPM.
• If you want developer-centric orchestration with strong reliability, look at Temporal, but expect to build more of the human-task layer yourself.
• If your use case is more data pipeline orchestration, look at Airflow/Prefect/Dagster, though they’re less natural for business approvals.

If you want, I can also give you a shortlist by use case (for example: mainframe integration, SAP/Oracle integration, customer service workflows, or regulated approvals).