It targets free pascal only.
But don't let that stop you, as fp has added a lot of new language features like:
- implcit/explict conversions
- Value types can have methods, operators, and everything a class can have (except virtual methods, interface implementation)
- extension methods (again applies to value types as well as classes)
- c++ style operators (++,--,+=.*=, ect)
- operator overloading
- inlining code
- generics with constraints
- much improved reflection (they call it rtti)
- managed types (dynamic arrays, interfaces, dynamics)
- and a lot more
It also is native code which is great for interfacing with the open source software it is build on (sdl2, opengl, openssl, libxml). Direct memory pixel (use for sprite collision) or vertex buffer (vertex data is a pointer to a user defined data in memory) access is very easy.
Also it includes the Lazarus IDE which I briefly overview in this video, includes stepping into dlls C code where you can see what the other open source frameworks are doing: