ddosim is a tool that can be used in a lab environment to simulate a distributed denial of service (DDOS) attack against a target server. The test will show the capacity of the server to handle application specific DDOS attacks. The tool is written in C++ and runs on Linux. Its current functionalities include: HTTP DDoS with valid requests with invalid requests (similar to a DC++ attack) SMTP DDoS flooding on random port.TCP connection flood on random ports.
Source: https://thehackernews.com/2011/01/ddosim-layer-7-ddos-simulator.html