TcUnit is currently the world's most popular PLC unit testing framework. It's being used by individuals and organizations across the whole globe. Maintaining and supporting TcUnit is done completely on volunteering work. Even though there are many companies using TcUnit to build better software, TcUnit is (and always will) be 100% free and open-source. However, as it takes a lot of time and resources to maintain TcUnit, the project would appreciate if you would consider supporting TcUnit.