Best Open Source APIs & Integration Tools in 2026

Warrant

Security & Monitoring APIs & Integration Developer Tools

Add RBAC, ABAC, and ReBAC to any app via API and SDK

stars 17license MITlang Go

Authorization API Infrastructure Developer Tools+4

Oso Cloud

Security & Monitoring APIs & Integration Developer Tools

Open source authorization with RBAC, ABAC, and ReBAC for any app

stars 3.5Klicense Apache-2.0lang Rust

Authorization Security Developer Tools+4

MuPDF

Developer Tools APIs & Integration Business & Productivity

Fast open source library for rendering and editing PDFs

stars 2.7Klicense AGPL-3.0lang C

Developer Framework API Development Tools Coding+3

Apache APISIX

APIs & Integration DevOps & CI/CD Cloud & Hosting

Cloud-native API gateway with dynamic routing and plugins

stars 16.5Klicense Apache-2.0lang Lua

API Infrastructure Cloud Native Authentication+5

Lago

Finance & Fintech APIs & Integration Backend Development

Usage-based billing API for metered and hybrid SaaS pricing

stars 9.6Klicense AGPL-3.0lang Go

API Infrastructure Invoicing & Payments Payment Infrastructure+4

Matrix

Communication & Collaboration APIs & Integration Security & Monitoring

Open protocol for secure, decentralized messaging and VoIP

stars 12.1Klicense Apache-2.0lang Python

Chat Security API Infrastructure+3

Centrifugo

APIs & Integration Backend Development Communication & Collaboration

Scalable real-time messaging server with WebSocket support

stars 10.2Klicense Apache-2.0lang Go

WebSocket Servers API Infrastructure Self Hosted+3

LiveKit

AI & Machine Learning APIs & Integration Communication & Collaboration

Real-time voice and video infrastructure on open source WebRTC

stars 10.2Klicense Apache-2.0lang Python

AI Agents API Infrastructure Developer Framework+5

Redis

Databases & Storage APIs & Integration Backend Development

High-performance open source in-memory data structure store

stars 74Klicense NOASSERTIONlang C

Database Self Hosted API Infrastructure+3

pdftk-java

Developer Tools APIs & Integration Business & Productivity

Java port of PDFtk for merging, splitting, and stamping PDFs

stars 2.2Klicense NOASSERTIONlang HTML

Developer Tools Coding API Development Tools+3

Ghostscript

Developer Tools IT Management APIs & Integration

Open source PDF and PostScript interpreter and converter

stars 226license NOASSERTIONlang C

Developer Tools Workflow Automation Coding+3

Meilisearch

Data & Analytics Developer Tools APIs & Integration

Typo-tolerant search engine with instant results, one binary

stars 57.4Klicense NOASSERTIONlang Rust

Search Engine AI Search Tools Self Hosted+4

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Oso Cloud

MuPDF

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Matrix

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pdftk-java

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Warrant

Oso Cloud

MuPDF

Apache APISIX

Lago

Matrix

Centrifugo

LiveKit

Redis

pdftk-java

Ghostscript

Meilisearch