GitHub
The largest hosted Git repository service, central to open-source collaboration since 2008 and owned by Microsoft since 2018.
GitHub is a web-based platform for hosting Git repositories and collaborating on source code. It was launched in April 2008 by Tom Preston-Werner, Chris Wanstrath, P. J. Hyett, and Scott Chacon, building on the Git version control system that Linus Torvalds had created in 2005. Microsoft acquired GitHub in 2018 for approximately 7.5 billion USD in stock. By the mid-2020s the platform hosted more than 100 million developer accounts and hundreds of millions of repositories, making it the de facto centre of open-source software collaboration. GitHub's core value comes from layered network effects: a direct network effect (more contributors produce more code that more contributors discover and reuse) plus cross-side network effects between developers, employers, and dependent projects. Beyond hosting code it offers issue tracking, pull-request review, continuous integration via GitHub Actions, a package registry, security scanning, and GitHub Copilot (launched 2021), an AI pair-programmer trained on public repositories. The platform's role has provoked debates about hosting concentration, the implications of training large language models on public code, and the legal default that repositories without a LICENSE file are all rights reserved. GitHub is one of the canonical case studies in discussions of Network Effects in Knowledge Platforms.