The Open Source Software Development (OSSD) is a movement, challenges many traditional and commercial theories of software development. A group of developers, programmers, and other community members develop the Open Source Software (OSS) in a collaborative manner. Community and contributors provide great support to make the source code of the software easily understandable and modifiable. However, there are insignificant such standard model or methodologies for OSSD has yet been established. Currently, researchers are proposing methodologies in this area. This paper proposes a new model, OScrum by modifying the scrum to make it applicable for OSSD. The proposed model has been constructed after analyzing the key metrics, pillars, and values of Scrum and OSSD. The model has been evaluated through comparing implementation process and working procedure of OSSD. The result shows that the implementation process of OSCRUM has a very close relationship with the process of OSSD and therefore, it fits well in such software development.