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12 picks · data-backed ranking

Best open source apps written in Java

The best self-hosted apps written in Java are ElasticSearch, Keycloak and Halo. ElasticSearch leads with 78,420 GitHub stars.

Candidates: the 51 apps whose main GitHub language is Java.

Updated · data from GitHub, refreshed daily

Top picks

  1. Rank 1:

    ElasticSearch

    elastic/elasticsearch

    Distributed, RESTful search and analytics engine.

    Active · last commit Oct 28, 2026

    Search EnginesJava

    Stands out for the most GitHub stars. ElasticSearch has 78,420 GitHub stars, uses the AGPL-3.0, SSPL 1.0 or Elastic License 2.0 (your choice) license, is written in Java and had 14,809 commits in the last year; it replaces Algolia.

  2. Rank 2:

    Keycloak

    keycloak/keycloak

    Open-source identity and access management with SSO, OIDC, SAML and user federation.

    Active · last commit Oct 28, 2026

    Identity & SSOJavaDocker

    Stands out for a permissive Apache-2.0 license. Keycloak has 37,563 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 3,232 commits in the last year; it replaces Auth0 and Okta.

  3. Rank 3:

    Halo

    halo-dev/halo

    A powerful and easy-to-use website building tool (documentation in Chinese).

    Active · last commit Oct 27, 2026

    Low-code & BackendJavaDocker

    Stands out for the most recent release (v2.27.1, October 2026). Halo has 40,071 GitHub stars, uses the GPL-3.0 license, ships a Docker image, is written in Java and had 627 commits in the last year.

At a glance

Open source apps written in Java compared

Ranked on GitHub stars, commits in the last year, Docker images, open-source licenses and recent commits. Projects with fewer than 12 commits in the last 12 months rank below every more active project.

Top 10 picks compared, data as of Oct 28, 2026
AppStands out forLicenseGitHub starsCommits (12 mo)Last commitDocker image
ElasticSearchthe most GitHub starsAGPL-3.0, SSPL 1.0 or Elastic License 2.0 (your choice)78,42014,809Oct 28, 2026No
Keycloaka permissive Apache-2.0 licenseApache-2.037,5633,232Oct 28, 2026Yes
Halothe most recent release (v2.27.1, October 2026)GPL-3.040,071627Oct 27, 2026Yes
Kestrathe newest codebase (created August 2019)Apache-2.030,0445,218Oct 28, 2026Yes
Jenkinsa permissive MIT licenseMIT26,7031,140Oct 28, 2026Yes
Mindustry–GPL-3.029,5032,009Oct 22, 2026No
Apache SkyWalking–Apache-2.024,976279Oct 28, 2026Yes
OneDev–MIT15,3291,058Oct 28, 2026Yes
LanguageTool–LGPL-2.115,2052,065Oct 28, 2026Yes
SuperTokens–Apache-2.015,335874Oct 28, 2026Yes

Full ranking

All 12 picks, ranked

Ranked on GitHub stars, commits in the last year, Docker images, open-source licenses and recent commits. Projects with fewer than 12 commits in the last 12 months rank below every more active project.

  1. 1

    ElasticSearch

    Distributed, RESTful search and analytics engine.

    Stands out for the most GitHub stars. ElasticSearch has 78,420 GitHub stars, uses the AGPL-3.0, SSPL 1.0 or Elastic License 2.0 (your choice) license, is written in Java and had 14,809 commits in the last year; it replaces Algolia.

  2. 2

    Keycloak

    Open-source identity and access management with SSO, OIDC, SAML and user federation.

    Stands out for a permissive Apache-2.0 license. Keycloak has 37,563 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 3,232 commits in the last year; it replaces Auth0 and Okta.

  3. 3

    Halo

    A powerful and easy-to-use website building tool (documentation in Chinese).

    Stands out for the most recent release (v2.27.1, October 2026). Halo has 40,071 GitHub stars, uses the GPL-3.0 license, ships a Docker image, is written in Java and had 627 commits in the last year.

  4. 4

    Kestra

    Event-driven, language-agnostic platform to create, schedule, and monitor workflows. In code. Coordinate data pipelines and tasks such as ETL and ELT.

    Stands out for the newest codebase (created August 2019). Kestra has 30,044 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 5,218 commits in the last year; it replaces Zapier.

  5. 5

    Jenkins

    The leading open-source automation server for building, testing and deploying software.

    Stands out for a permissive MIT license. Jenkins has 26,703 GitHub stars, uses the MIT license, ships a Docker image, is written in Java and had 1,140 commits in the last year; it replaces GitHub Actions / CircleCI.

  6. 6

    Mindustry

    Factorio-like tower defense game. Build production chains to gather more resources, and build complex facilities.

    Mindustry has 29,503 GitHub stars, uses the GPL-3.0 license, is written in Java and had 2,009 commits in the last year.

  7. 7

    Apache SkyWalking

    Application performance monitoring and observability platform for distributed systems.

    Apache SkyWalking has 24,976 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 279 commits in the last year.

  8. 8

    OneDev

    All-In-One DevOps Platform. With Git Management, Issue Tracking, and CI/CD. Simple yet Powerful.

    AI-nativeOneDev has 15,329 GitHub stars, uses the MIT license, ships a Docker image, is written in Java and had 1,058 commits in the last year; it replaces GitHub and GitLab.

  9. 9

    LanguageTool

    Proofread more than 20 languages. It finds many errors that a simple spell checker cannot detect.

    LanguageTool has 15,205 GitHub stars, uses the LGPL-2.1 license, ships a Docker image, is written in Java and had 2,065 commits in the last year.

  10. 10

    SuperTokens

    Open-source authentication with login, sessions and social sign-in for your own app.

    SuperTokens has 15,335 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 874 commits in the last year.

  11. 11

    Druid

    Distributed, column-oriented, real-time analytics data store.

    Druid has 14,096 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 1,438 commits in the last year.

  12. 12

    OpenSearch

    Distributed and RESTful search engine.

    OpenSearch has 13,919 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 1,464 commits in the last year; it replaces Algolia.

FAQ

Questions and answers

Still curious? Email info@appsgit.com.

Is ElasticSearch free?

Yes. ElasticSearch is open-source software released under the AGPL-3.0, SSPL 1.0 or Elastic License 2.0 (your choice) license, so you can self-host it at no cost. You only pay for the server it runs on, and some projects also offer an optional paid cloud plan.

Can I self-host these apps with Docker?

Yes, 10 of the 12 picks. Keycloak, Halo and Kestra publish Docker images, so you can run them on a VPS or home server with Docker Compose. The others install from their own packages or source; follow each project's install guide.

Are all of these apps open source?

All 12 apps on this list are open source. You can self-host and modify each one under its license.

Which of these apps is the most actively developed?

ElasticSearch, with 14,809 commits in the last 12 months and a latest release, v9.5.5, from October 2026. Activity is a good sign that bugs and security issues get fixed.

How is this list ranked?

Ranked on GitHub stars, commits in the last year, Docker images, open-source licenses and recent commits. Projects with fewer than 12 commits in the last 12 months rank below every more active project.

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