Open Source development model has greatly changed how the software projects are handled & developed. It encourages open collaboration, knowledge sharing between huge developer communities,.. that further results in development & improvement of the end product.
There are numerous OSS (Open Source Software) projects on Github that can be quoted to show how successful this development model has turned-out to be. Even huge corporate companies have started to run their propitiatory software development through OSS model & changed pricing model as subscription based services.
Here is the list of leisure time projects through which I've contributed back to the Open Source community and felt worth mentioning over here