In recent years, the research community has become increasingly interested in automated negotiation. It has been used in real-world systems such as autonomous vehicle transportation systems, smart grids, and e-commerce. Considering the broad range of applications, automated negotiation is of great use and interest to engineers, developers, and industry-focused researchers. Therefore, some researchers have developed platforms for automated negotiation. However, these systems do not provide complete control over the development of various protocols or analytic tools. This paper introduces NegoSim, a new negotiation simulator that introduces a new negotiation framework called EUBOA, though it also works on the well-known BOA framework. NegoSim is completely modular, with different APIs allowing users full control over developing and modifying automated negotiation agents, different assessments, protocols, and utility spaces, as well as the ability to create or modify different GUIs. NegoSim also includes predefined agents, protocols, utility space, and analytic tools, making it an ideal platform for researchers.