Meet Unleash at one of the events we're attending this year➩ See where we'll be
Unleash
13.7k

Watch "Implementing a Kill Switch for AI"

Events

Join the Unleash team to learn how to integrate runtime control in your AI strategy.

11 Open-source feature flag tools

Michael Ferranti

Michael Ferranti

VP of Strategy

August 10, 2026

Comparison of 11 open-source feature flag tools

11 Open-source feature flag tools

Hello and welcome to an overview of 11 open-source feature flag tools. We love feature flags here, and we love open-source! We feel strongly that the more developers can adopt these 2 concepts, the better we are as an industry. We’ve made this handy list of 11 open-source feature flag tools to help you in your feature flag journey.

TL;DR

  • Some of these tools are language-specific, others language-agnostic.
  • Several focus on A/B testing, others only flag control.
  • Hosting varies between cloud, self-hosted, or hybrid.
  • Licenses range from MIT to Apache to GPL.
  • Pricing spans free tiers to enterprise subscriptions.
  • Feature depth differs from lightweight daemons to full platforms.

Read our FeatureOps Whitepaper

Get your free copy and learn how to connect engineering performance to business outcomes for fun and profit.

Download now

What is Unleash

Hello, we’re Unleash, and our mission is to make life easier for developers. We’re an open-source Feature Management platform, i.e., we’re a really good way to help you use feature flags. This makes releasing new features less risky, and streamlines the software release process. Unleash can be used as a private hosted cloud instance or as a self-hosted solution, if you prefer that or need Fed Ramp or Air-Gapped use cases. The Unleash repo has over 10,000 GitHub stars and has been downloaded over 20 million times.

Why we made Unleash

In 2014 Ivar was working as a software developer at FINN.no, Norway’s largest online marketplace. Getting new features into production was a pain, so, as a developer, he looked around and wondered if he could write some code to make it easier. The initial goal was to protect features under development, allowing our team to transition to trunk-based development.

10 years later, he’s CTO of Unleash, and we’re the leading open-source feature flag solution. We serve the world’s largest, most security-conscious organizations, and we’re even rated the “Easiest Feature Management system to use” by G2.

Open source feature flag tools

Here’s our list of open source feature flag tools:

Unleash

It’s us! We obviously think you should choose Unleash, but feature flags make everyone’s software better, and we want to live in a better world.

Featbit

  • Pricing Page: https://dashboard.featbit.co/
  • Free tier and enterprise plan for $3,999/year for self-hosting. $49.9, $399 and enterprise plans for cloud offering.

FeatBit is an open-source feature flag and A/B testing platform. It provides a self-hosted and a cloud solution for managing feature flags and running experiments.

FF4J

FF4J (Feature Flipping for Java) is an open-source feature flag framework for Java applications and other JVM languages. The framework includes a web console for managing flags and monitoring their status.

Flagsmith

  • Pricing Page: https://www.flagsmith.com/pricing
  • Free up to 50,000 reqs/month (1 user, 1 project), then $45 up to 1M reqs/month (3 users, unlimited projects). Enterprise plans available.

Flagsmith is a feature flag and remote configuration service. It offers a platform for managing feature flags, remote config, and A/B testing.

flagd

Flagd is an open-source feature flagging daemon. Flagd can be run as a sidecar container in Kubernetes or as a standalone service.

Flagr

Flagr is a feature flagging, A/B testing and dynamic configuration microservice written in Go. It was originally developed by Checkr and then open-sourced later.

Flipper

Flipper is an open-source tool for managing feature flags in Ruby applications. Flipper supports integration with different data stores like Redis and ActiveRecord. It’s commonly used in Rails projects.

Flipt

Flipt is an open-source feature flag management solution. Its cloud offering is currently under development.

Go Feature Flag

GO Feature Flag is an open-source, feature flag management solution written in Go (obviously). GO Feature Flag supports gradual rollouts, user targeting, and A/B testing.

GrowthBook

GrowthBook is an open-source feature flagging and experimentation platform.

PostHog

PostHog is an open-source product analytics and experimentation platform. It includes a feature flag service.

FAQs about open source feature flag tools

What are the primary advantages of using open-source feature flag tools?

Open-source feature flag tools promote transparency and community-driven development, often leading to robust and flexible solutions. Additionally, many open-source options provide cost-effective self-hosting capabilities, offering greater control over data and infrastructure than cloud-hosted feature flag solutions.

How do the licensing and pricing models typically vary among open-source feature flag tools?

Apache, MIT, and GPL, for example, each determine their own usage and distribution rights. While core functionality is often free for self-hosting, many projects offer paid tiers or managed cloud services. These commercial options typically include enhanced features like advanced security, enterprise support, or additional environments beyond the basic open-source offering.

What criteria should teams consider when selecting an open-source feature flag solution?

When choosing an open-source feature flag solution, teams should evaluate factors like…

  • Community activity and GitHub star count, indicating project vitality and support.
  • Breadth of supported SDKs and programming languages, ensuring compatibility with existing tech stacks.
  • Features like A/B testing capabilities
  • Remote configuration, and flexible hosting options to meet their operational needs.

Can open-source feature flag tools like Unleash integrate with existing development workflows?

Yes, open-source feature flag tools are generally designed for seamless integration into existing development workflows and CI/CD pipelines. They typically offer client and server-side SDKs, enabling developers to easily incorporate feature toggles into their applications.

Explore further