The free version of FL Studio, known as the Demo version, allows you to use all the features of the software, but it has some limitations, such as not allowing you to reopen saved projects after closing the program. The paid versions (Producer, Signature, and All Plugins) offer full functionality, including the ability to reopen projects, access to more plugins, and lifetime free updates. Each tier also includes different sets of additional features and tools, catering to various needs and budgets.