You need a botnet to do real massive attacks, if you don't want to create a botnet, you will have BIG PROBLEMS, but, at last
https://www.blackhatrussia.com/1710-layer-4-ddos-tool-python.html
https://www.blackhatrussia.com/1739-hulk-v3-ddos.html
https://www.blackhatrussia.com/1290-denial-of-service-dos-mega-pack.html