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.
Ranked in these QuestionsQuestion Ranking
Pro Lightweight without losing functionality
The framework is very lightweight and fast. Even though it's pretty light, it still does not lose a lot of functionality.
Pro Highly modular
Virtually everything is modular. You can choose which modules and libraries to include and to keep the framework as lightweight as possible.
Pro Comprehensive and excellent documentation
Pro ORM supports sql, nosql, and jig
Pro No canned coding/directory structure
Freedom to structure your projects' directories and codes as you wish.
Pro Multiple View Engines
Default view engine is superb and can also work with varieties of PHP view engines including Twig.
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.