Best open source apps written in Java

1

ElasticSearch

Distributed, RESTful search and analytics engine.

Search Engines

78k

ElasticSearch has 78,194 GitHub stars, uses the AGPL-3.0, SSPL 1.0 or Elastic License 2.0 (your choice) license, is written in Java and had 13,336 commits in the last year; it replaces Algolia.

2

Keycloak

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

Identity & SSODocker

37k

Keycloak has 37,156 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 3,157 commits in the last year; it replaces Auth0 and Okta.

3

Halo

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

Low-code & BackendDocker

40k

Halo has 39,927 GitHub stars, uses the GPL-3.0 license, ships a Docker image, is written in Java and had 580 commits in the last year.

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.

Automation & WorkflowsDocker

29k

Kestra has 29,274 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 4,392 commits in the last year; it replaces Zapier.

5

Jenkins

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

CI/CD & DeploymentDocker

27k

Jenkins has 26,618 GitHub stars, uses the MIT license, ships a Docker image, is written in Java and had 1,159 commits in the last year; it replaces GitHub Actions / CircleCI.

6

Mindustry

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

Games

29k

Mindustry has 29,232 GitHub stars, uses the GPL-3.0 license, is written in Java and had 1,920 commits in the last year.

7

Apache SkyWalking

Application performance monitoring and observability platform for distributed systems.

Monitoring & Status PagesDocker

25k

Apache SkyWalking has 24,967 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 265 commits in the last year.

8

LanguageTool

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

UtilitiesDocker

15k

LanguageTool has 15,107 GitHub stars, uses the LGPL-2.1 license, ships a Docker image, is written in Java and had 1,930 commits in the last year.

9

Druid

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

AnalyticsDocker

14k

Druid has 14,059 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 1,223 commits in the last year.

10

OpenSearch

Distributed and RESTful search engine.

Search EnginesDocker

14k

OpenSearch has 13,815 GitHub stars, uses the Apache-2.0 license, ships a Docker image, is written in Java and had 1,370 commits in the last year; it replaces Algolia.

11

OneDev

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

Project ManagementDocker

15k

AI-nativeOneDev has 15,281 GitHub stars, uses the MIT license, ships a Docker image, is written in Java and had 608 commits in the last year; it replaces GitHub and GitLab.

12

Thingsboard

IoT Platform - Device management, data collection, processing and visualization.

Source-availableHome Automation & IoTDocker

23k

Thingsboard has 22,512 GitHub stars, is source-available under the BSL 1.1 (not an open-source license), ships a Docker image, is written in Java and had 3,539 commits in the last year.