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Lets you build your own design pattern unlike other frameworks with already MVC pattern built-in. Easy to learn and thanks to clear documentation. One big plus for me is the easy to learn ORM feature that supports sql, and nosql. I can no longer worry about using both db or switching from one to another bec my orm code will be the same; just change db settings.
SpecsUpdate
Pros
Pro Comprehensive documentation and API reference
Concise and to the point documentation. Includes many examples and complete API reference @ https://fatfreeframework.com/3.6/api-reference
Cons
Con Default ORM doesn't support joins
The default ORM for this framework is missing some features such as joins. But it's important to keep in mind that it's a small plugin, only 23KB in size which still can be replaced with a larger ORM if needed.
An alternative the drop in f3-cortex ORM which is popular, and supported by the community, which supports Joins and much more.