head to head · open source
haystack vs flowable-engine
haystack has 26,559 GitHub stars, 3,153 forks, 143 open issues and last shipped yesterday. flowable-engine has 9,542 stars, 2,890 forks, 411 open issues and last shipped 3 days ago. haystack leads on adoption by 178% (26,559 vs 9,542 stars). haystack is written in Python under Apache-2.0; flowable-engine is written in Java under Apache-2.0. haystack has attracted 12% as many forks as stars, flowable-engine 30%. haystack was the more recently maintained of the two, and both are self-hostable with no licence fee.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| haystack | flowable-engine | |
|---|---|---|
| GitHub stars | ★ 27K | ★ 9.5K |
| License | Apache-2.0 | Apache-2.0 |
| Written in | Python | Java |
| Last push | 2026-09-19 | 2026-09-17 |
| Forks | ⑂ 3.2K | ⑂ 2.9K |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick haystack if
- You weight community size — 27K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches Python
- You value the larger contributor base for long-term maintenance
pick flowable-engine if
- You want the flowable-engine feature set and don't need the biggest community
- You prefer the Apache-2.0 license terms
- Your stack matches Java
- You evaluated both and flowable-engine fits your workflow better
About haystack
Haystack is an open source AI orchestration framework written in Python under the Apache 2.0 licence, for building context engineered, production ready large language model applications as modular pipelines and agent workflows with explicit control over retrieval, routing, memory, and generation, and it is aimed at developers and teams building scalable agents, retrieval augmented generation, multimodal applications, semantic search, question answering, and conversational systems.
read the full haystack overview →
About flowable-engine
Flowable is an open source workflow and Business Process Management platform written in Java and distributed under the Apache 2.0 license. It bundles three engines in one project: a BPMN process engine, a CMMN case engine, and a DMN rule engine. The project lives in the Java ecosystem, integrates with Spring, and exposes both a Java API and a REST API for orchestrating human or system activities.
read the full flowable-engine overview →
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Frequently asked questions
Is haystack or flowable-engine more popular?
haystack has 26,559 GitHub stars and flowable-engine has 9,542. haystack has the larger community by that measure.
Are haystack and flowable-engine free?
Both are open source. haystack is licensed under Apache-2.0 and flowable-engine under Apache-2.0. Neither carries a licence fee.
What is the difference between haystack and flowable-engine?
haystack is written in Python and flowable-engine in Java. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, haystack or flowable-engine?
Choose haystack if you want the larger community (26,559 stars) or its Apache-2.0 licence terms. Choose flowable-engine if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.