- Microsoft has participated in various open source projects since the early 2000s including AIDS vaccine research tools and Windows Live APIs for online and classroom learning. - Open source projects have large communities with Port25 receiving 2 million unique visitors and Codeplex having over 40,000 registered users and 5,000 projects. - While the top 10 open source projects are widely known, there are over 180,000 total open source projects with around 50% being used on Windows platforms.