For a new project with Flash I was looking for something along the lines of standard libraries for basic programming needs, along the lines of Python or Ruby standard libraries. But the only thing I found was a dead project on Sourceforge.
Thus is there no standard library for flash? Does everyone reinvent the wheel each time?
The basic libraries are built into flash. Then on top of that there is flex, which gives you an entire RIA framework. Then there are 3rd party frameworks for 3d, physics engines, various design patterns (MVC, IoC etc) to name just a few.
So no, you do not not to reinvent the wheel every time.
Assuming I understand your question correctly, the Flash Player API is the "standard library" for Flash applications (the flash.* packages).
For more application programming -oriented libraries, there are the Flex standard libraries (the mx.* packages).