Magento is currently the largest open-source eCommerce platform in the world. Due to its feature rich and extensible code base, merchants with large and small operations all around the world have been using it for a wide variety of projects.
Magento 1 has been around for eight years, and its successor, Magento 2, was released at the end of 2015, improving weak points of the earlier version such as improved performance, official automated test suite, enhanced back-end UI including a new modern front-end codebase.
It is also a modular way to develop modules, with files contained inside the Magento code instead of being scattered all over the place. Moreover, Magento reduces the number of conflicts between modules trying to customize the same functionality.