The main difference between these is knowing your preference between building a brand new test automation framework using libraries or working with a made-ready tool where testing is all you will have to care about.

This article gives you a quick glance at the top 10 free and open-source testing tools, frameworks, and libraries.

1. Katalon Studio

Katalon Platform - Opensource testing tool

Katalon Studio is a popular and free test automation tool for web, mobile, API and desktop (Windows). Offering both low-code and scripting methods, Katalon removes the complicated training to build and maintain a separate testing framework.

With everything built-in, users can focus directly on testing activities and spend less effort on creating, running and maintaining tests.

Feature highlights:

Supported programming languages: Java and Groovy
OS compatibility: Windows, macOS, and Linux
Flexible and fast test creation with Record and Playback, Manual and Script Mode
Debugging UI and smart reporting to troubleshoot failed tests
Reusable test artifacts (test cases, objects, keywords, etc.) with the Page Object Model (POM) design and Test Artifact Sharing
Supported testing methodologies: BDD, DDT, Keyword-Driven Testing, Cross-Browser Testing (Headless, Chrome, Edge, Firefox, and Safari), and Cross-Platform Mobile Testing (iOS, Android)
Allow importing Selenium, SoapUI, and Postman projects
Native integrations to CI/CD systems (Jenkins, Bamboo, Azure DevOps, CircleCI, etc.), ALMs (e.g., Jira)
Step-by-step tools training to use Studio in real projects on Katalon Academy

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2. Selenium

Selenium is probably the first name that pops up on the subject of web-based and open-source test automation. To be more exact, Selenium wouldn’t be considered as a tool but an open-source library.

With the field-famous trifecta of Selenium WebDriver, Selenium IDE, Selenium Grid, and the recent release of Selenium 4.7.0, this is sure to be the top choice for coding enthusiasts.

Feature highlights

Supported programming languages: Java, JavaScript (Node.js), Groovy, Scala, PHP, Perl, Python, Ruby, or C#
Import advanced tests scripted on Eclipse, Visual Studio, or NetBeans
Compatible with macOS, Windows, and Linux for cross-platform execution
Customizable add-ons and plugins
Allows integration with frameworks such as Ant, Maven, TestNG, JUnit, NUnit, etc.

Website: Selenium

3. Appium

Sharing a similar suffix as Selenium’s, Appium is likewise the open-source framework to remember for automated mobile testing. From native, mobile web to hybrid applications, Appium is a highly sought-after option to eliminate the need for recompiling applications and automating APIs.

Feature highlights

Supported programming languages: Java, PHP, Objective-C, C#, Clojure, JavaScript with Node.js, Python, Perl, or C#, whichever Selenium supports
JSON Wire Protocol to add flexibility to the programming language used
Automated testing scripts can run on iOS and Android platforms
Test applications without having the source code in place

Website: Appium

4. Apache JMeter

Apache JMeter, or JMeter in short, is an automation tool for performance (load and stress testing) and functional testing. JMeter’s primary uses are to measure the performance of applications and act as virtual users to send requests to the designated server.

Feature highlights

Supported programming language: Java
User-friendly UI/GUI and Beanshell processor for custom code
Works with HTTP, HTTPS, JDBC, LDAP, FTP, LDAP, SOAP, POP3, IMAP, SMTP, TCP, and Java-scripted protocols
Open to integrating with Jenkins and third-party reporting tools
Multi-threaded framework (Concurrency Thread Group) to sample functions separately from a thread group

Website: Apache JMeter

5. SOAP UI

To test SOAP and REST APIs, we got SOAP UI. Aside from API testing, SoapUI’s open-source application for web service testing additionally covers functional, load, compliance, and mock testing.

Feature highlights

Supported programming languages: Groovy and Javascript
Protocol support for SOAP/WSDL, REST, and JMS
DataSource TestStep for Data-Driven Testing
Simple requirements management
Integration with Maven, HUDSON, JUnit, and Apache Ant

Website: SoapUI

Get 5 more API testing tools: Top 15 Automated API Testing Tools in 2024 | Latest Update

6. Robot Framework

Robot Framework.png

Using Python as the main scripting language, Robot Framework is an open-source framework for acceptance testing and robotic process automation (RPA). The Robot Framework is commonly associated with free mobile and desktop applications testing tools.

Feature highlights

Supported programming language: Python, Jython (Java), PyPy, and IronPython (.NET)
OS compatibility: Windows, macOS, Unix, and Linux
Can use Eclipse, RIDE (Robot Framework IDE), or text editors to build tests
Keyword-driven testing, autocomplete completion, and syntax highlighting to reduce coding time
Integration with Appium and Selenium

Website: Robot Framework

7. Watir

Watir, or Web Application Testing in Ruby, provides you with open-source libraries in Ruby for cross-browser or web test automation. Watir uses Selenium under the hood, so it's able to utilize Selenium's common API.

Feature highlights

Supported programming language: Ruby
Browser compatibility: Chrome, Firefox, Edge, Internet Explorer, Safari
BDD design is available from integrations with Cucumber, RSpec, etc.
Watir 7.2 is available on RubyGems but requires Ruby 2.7 and Selenium 4.2

Website: Watir

8. JUnit

Java plus unit testing gives us JUnit. Ranking 7th in Java Top 10 Libraries, this free open-source testing framework is a favorite among Java developers to edit and refactor code at the unit level. What’s more, the release of JUnit 5 has brought useful updates like better organizing tests in hierarchies, simultaneous use of multiple runners at once, and more.

Supported programming language: Java
Script automated unit tests with annotations and assert classes
Extension APIs or extension mechanisms to work with third-party software
Parallel execution (version 5.3 onwards)
AssertThrows method for easier exception and timeout handling

Website: JUnit

9. Robotium

Often referred to as the “Selenium for Android,” Robotium is a popular open-source framework for Android applications black-box testing, both native and hybrid.

Supported programming language: Java
Run-time binding to view all Android UI components and activities
Integration with Gradle, Maven, and Ant to write automated mobile tests
Adjustable execution speed with Config.sleepDuration and Config.sleepMiniDuration

Website: Robotium

10. Citrus

Our last open-source test automation framework is Citrus. Citrus would definitely ring a bell for developers working with integration testing and verifying messaging transport connectivity. As well as that, connecting JUnit or TestNG to use in complementary is common to script Java-based unit tests.

Supported message protocols: HTTP, REST, SOAP, Kafka, JMS, etc.
XML or Java coding for flexible test creation
Integration with Apache Camel, Arquillian, Kubernetes, and Docker to enable microservice integration testing
BDD and cloud-native BDD automated testing using Cucumber and YAKS
Test POST, GET, PUT, DELETE, OPTIONS, PATCH, HEAD, and REST APIs with REST’s extension

Website: Citrus

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Vendor tools or open-source frameworks?

If you’re wondering which testing tool is best, it’s worth pausing to consider the context first.

Key Questions to Ask:

What are you testing? Is your focus on web, mobile, API, desktop, or multiple platforms? Remember, a tool suited for unit testing won’t necessarily cover functional testing needs.
Who handles testing? If developers are doing most of the testing, building a custom framework may be practical. However, if QA engineers lead testing, Katalon Studio can help streamline work. It frees up developers for core development tasks while allowing QA teams to focus on end-to-end testing.
Can the tool support team growth? As your team scales, integrations with CI/CD, DevOps, and Agile tools become essential. For open-source frameworks, each integration can require significant setup. With Katalon, however, integrations are built-in, enabling quick setup so you can get back to testing faster.
How easy is it to update? For example, moving from Selenium 3 to Selenium 4 requires migrating all tests, a time-intensive process. In contrast, Katalon Studio updates with a simple “Upgrade Now” button, giving you immediate access to new features without hassle.