Open Source software is a software that has "open code", that is published and can be modified by anyone. Open Source software has gained popularity in the last 10 years mainly due to the understanding that Open Source software, supported by a community of users, is cheaper and better than proprietary software. Most of the Open Source systems are free, and the cost involved in using them relates only to installation costs, training and potential support.
The most popular Open Source software for website management, data management, office productivity tools or operating systems have users counting in the millions and usually several hundreds of thousands of active contributors, constantly improving and testing the software. Open Source software usually allows easy import/export of data which means the flexibility to change the system as needed, without having to pay hefty prices for a similar process performed with proprietary (closed) source systems.
Another benefit of using Open Source system is being able to rely on a large community of developers - which provides better continuity of support for the system, in case the original contractor is no longer available to support the product.
Finally, and in our belief, most importantly, the value of using Open Source system, is being part of the community of users/testers - who, by providing feedback on the product, are an important part of the Open Source ecosystem, making it better for one's own use and fellow users.