Below are open-source integration platforms and related projects that large enterprises commonly use (each entry includes what it does best, enterprise strengths, license/notes, and a short use-case). I cite vendor/project pages so you can verify current features, releases and licensing.

1. Apache Camel — integration framework / EIP library

• What it is: A mature Java-based integration framework implementing Enterprise Integration Patterns; runs standalone or embedded (Spring Boot, Quarkus, Camel K, etc.). (camel.apache.org)
• Strengths: Extremely large component ecosystem (connectors), flexible DSLs, embeddable, good for application-to-application orchestration and routing logic.
• License / enterprise notes: Apache 2.0, wide community and long-term stability.
• Good for: Complex routing/mediation inside services, microservice message choreography, platform-embedded integration.

2. Apache NiFi — dataflow / event & file movement

• What it is: GUI-driven dataflow engine for routing, transforming, and tracking data provenance with back-pressure and guaranteed delivery. (nifi.apache.org)
• Strengths: Visual flow designer, provenance (lineage), strong for high-throughput streaming/batch flows, enterprise security features.
• License / enterprise notes: Apache 2.0; used broadly in telecom, gov, big-data ingestion pipelines.
• Good for: Streaming ETL, ingest pipelines, IoT telemetry, secure file/sensor/event routing.

3. Apache Kafka (Connect + Stream processing) — event streaming + connectors

• What it is: Distributed event streaming platform; Kafka Connect provides pluggable source/sink connectors; Kafka Streams / ksqlDB for processing.
• Strengths: High throughput, durable event log, ecosystem for streaming integration (CDC, connectors), excellent for event-driven architectures.
• License / enterprise notes: Apache 2.0 (Kafka) and many vendor-managed distributions; often paired with Confluent components for enterprise features.
• Good for: Event-driven integration between systems, CDC, real-time analytics, streaming ETL.
• (See Apache Kafka project pages and Kafka Connect ecosystem for connector options.)

4. WSO2 Enterprise Integrator (Micro Integrator + Streaming Integrator)

• What it is: Open-source hybrid integration platform providing ESB-style mediation, micro-integrator runtime, API management integrations and streaming (Siddhi). (github.com)
• Strengths: Visual tooling, many connectors, streaming SQL engine (Siddhi) for real-time processing, cloud-native deployments.
• License / enterprise notes: Apache-2.0 for many components; WSO2 offers commercial support and enterprise distributions.
• Good for: Organizations wanting an integrated ESB/API/streaming stack with vendor support options.

5. Airbyte — open-source data integration (ELT) platform

• What it is: Open-source ELT/data-sync platform with a large and growing connector catalog, focused on moving data into data warehouses/ lakes/ vector stores. (Airbyte.com)
• Strengths: Fast connector development, modern UX, strong community, designed for analytics/data-team use cases, enterprise features in paid tier.
• License / enterprise notes: Core is open-source; paid enterprise/cloud options add governance, support and hosted services.
• Good for: Analytics ingestion, data warehouse syncs, building data pipelines for ML/BI.

6. Tyk / Kong (open-source API gateways) — API management & integration building block

• What they are: Open-source API gateways that provide routing, security, policies and plugin extensibility for APIs (Kong and Tyk are leading OSS gateways). (konghq.com)
• Strengths: High-performance proxying, plugin ecosystems, policy enforcement, useful as the API façade for integration surfaces.
• License / enterprise notes: Both projects have open-source cores and commercial enterprise offerings for advanced features/support.
• Good for: Securing and governing APIs, rate-limiting, traffic shaping and acting as the integration entry point.

7. Talend Open Studio (and Talend components)

• What it is: Long-standing open-source data integration/ETL tooling (Talend Open Studio), with a commercial enterprise platform that adds governance, scheduling, and support.
• Strengths: Visual ETL, many connectors, good for batch ETL and data quality tasks.
• License / enterprise notes: Open-studio is OSS; enterprise features require Talend commercial editions.
• Good for: Traditional ETL/data warehouse integration and data-migration projects. (nifi.apache.org)

8. Debezium (CDC) + other connector projects

• What it is: Open-source Change Data Capture (CDC) connectors (Debezium) that integrate with Kafka Connect or other pipelines to stream DB changes.
• Strengths: Reliable CDC for syncing DB changes to downstream systems, often used alongside Kafka Connect/NiFi/Airbyte.
• Good for: Near-real-time replication, event-driven apps, eliminating polling-based integrations.

Additional notes on architecture and choices

• Most large enterprises use a mix of the above rather than one monolithic “integration platform.” Typical patterns: API gateway (Kong/Tyk) for transactional integrations; Kafka + Connect + stream processing for event-driven flows; NiFi for data-heavy ingestion and provenance; Camel or WSO2 for message mediation and per-application routing; Airbyte/Talend for analytics/ETL. (See the project pages above for details.) (camel.apache.org)
• Licensing & vendor lock: confirm each project’s current license and the boundary between OSS core and paid enterprise features — many projects keep a feature-rich paid offering while maintaining an OSS core (Kong, Tyk, Airbyte, Talend, etc.). Use vendor pages / GitHub repos to validate exact license/version for your chosen release. (github.com)
• Support & hardening: For critical enterprise workloads you’ll usually want a vendor-supported distribution or an in-house SRE/Platform team to manage upgrades, HA, security patches, observability and multi-region deployments.

Quick selection checklist (practical criteria)

• Integration pattern fit: transactional APIs vs streaming vs batch ETL vs CDC.
• Throughput/latency requirements: Kafka/NiFi for high-throughput streaming; API gateways for low-latency REST/RPC.
• Observability & provenance: NiFi and Kafka provide strong lineage/offset tracking.
• Connectors & extensibility: Camel, Airbyte, Kafka Connect have large connector ecosystems.
• Security/compliance & enterprise SLAs: plan for supported distributions or commercial support.
• Cloud-native deployment: check Kubernetes operators/Helm charts and hardened images.

If you want, I can:

• Narrow this to 3–4 options tailored to your environment (cloud/on-prem, Java vs non-Java stack, event-driven vs ETL).
• Produce a short comparison matrix (features, scalability, licensing, rough TCO factors) with links to specific docs/releases.

Which would you like next?