No. 11 of 24 ·Stream Processing Software

Esper

Windows · Linux · Self-hosted · API

Freedom report

Two barsScore 6.5

Free tierA free tier is on its own pricing page
Open codeNo open-source code on record
Runs widely2 of 6 device platforms
DocumentedPlans, terms and facts published

Esper is ranked #11 of 24 in stream processing software on Freedom251. It runs on API, Linux, Self-hosted, Windows. There is a free plan.

Esper plans and pricing

All plans

Esper 9.0.0 Free GNU GPL (GPL v2) espertech.com · 3 Oct 2026

Esper support Not published per year and per instance or per seat Production support: Bronze, Silver, Gold · Development support: Developer Seat espertech.com · 3 Oct 2026

Compared on stream processing software

Free plan: Yes
Deployment model: self-hosted
SQL processing: Yes
Stateful processing: Yes
Event-time windows: Yes
Supported languages: Java, C#

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The record

Purpose: Esper is a language, compiler and runtime for complex event processing and streaming analytics, available for Java and .NET.
Event language: Its Event Processing Language (EPL) implements and extends SQL for expressions over events and time.
Compilation: The Esper compiler compiles EPL into bytecode that can be packaged in JAR files for distribution and execution.
Runtime: The runtime is an in-memory streaming engine that the site describes as memory-efficient and low-latency, and says does not require external storage or services.
Scale: Esper’s runtime has a horizontal scale-out architecture with elastic scaling, load balancing, fault tolerance and multi-datacenter support, built on Apache Kafka and Apache Zookeeper in Esper Enterprise Edition.
Integrations: The feature list names CSV, JMS, HTTP, Kafka, database and socket input/output adapters, and JMX metrics exposure.
External data: Esper supports joining external data, including web services, relational databases through SQL-query joins and method invocation joins.
Licensing: The downloads page lists Esper 9.0.0 under GNU GPL (GPL v2), and EsperTech says it offers commercial redistribution licenses for companies incorporating Esper or NEsper.
Enterprise security: Esper Enterprise Edition says EsperHQ and EsperJMX can access CEP engines remotely over secured connections with user credentials.
Support: EsperTech offers production support with Bronze, Silver and Gold service levels, and a Developer Seat for development questions.
Support limitation: Developer Seat support answers how-to questions and does not fix software bugs or provide training.
Target use cases: The site lists business process monitoring, financial applications such as fraud detection, network and application monitoring, and sensor network applications as typical uses.
Current release: The documentation page identifies Esper and EsperIO 9.0.0 as the current release.
Founded: 2006
Price from: Free

Where it ranks on Freedom251

Best Stream Processing Software in 2026#11 of 24

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Sources

espertech.com/esper/· checked 3 Oct 2026
espertech.com/esper/esper-downloads/· checked 3 Oct 2026
espertech.com/esper-enterprise-edition/· checked 3 Oct 2026
espertech.com/support/· checked 3 Oct 2026
espertech.com/esper/esper-documentation/· checked 3 Oct 2026