Open source libraries to design directed graphs

I'm going to need to write a program that takes a list of persons and connects them together in a directed-graph-like manner. The GUI aspect of the whole project is very important. The graph must allow a lot of interaction. Such as selecting several people and hiding the others, moving them around. Additionally, the software will need to be able to provide other kind of GUI-features such as several tabs, text boxes etc. The application must be quite efficient. As in, it must be able to handle hundreds if not thousands of widgets. Hence, I would like to know which open source libraries (at this point the programming language they are written in does not matter - I just want an overview of everything good that is out there) would allow me to develop such piece of software? What would you recommend? Edit: Could you please also link to tutorials explaining how I could program a GUI that can interact with the generated graph? For example mouse events.