Open Source Friday is an initiative by GitHub to encourage participation in open source projects, emphasizing its importance as both an industry standard and a strategic investment for companies. The program, which began with GitHub employees dedicating time every fourth Friday to contribute to open source, is now open to individuals, teams, and companies, with notable participants like Google, Microsoft, and Facebook. It provides a structured approach for contributions, supported by resources to help employees advocate for company involvement. GitHub also offers tools to track and share contributions, reinforcing the idea that supporting the software used by businesses is beneficial rather than purely altruistic.