SourceForge, launched in 1999 by the company VA Linux Systems, was the first big web platform built specifically for hosting open-source software projects. By its own account it is “an open source software community resource dedicated to helping open source projects be as successful as possible,” and it dates its founding to 1999 with, in its words, “over two decades of experience” building software development tools.
Its key idea was to gather, in a single hosted service, all the infrastructure a project needed. According to its own About page, SourceForge provides developers with code repositories and version control, binary hosting for downloads, bug tracking, download statistics, mailing lists, and discussion forums. Before this, a project that wanted those facilities typically had to assemble and run them itself on its own servers.
That bundling made it dramatically easier to start and run an open-source project. A maintainer could register, get a place to keep the code, a tracker for bugs, a way to distribute compiled releases, and a forum for users, without operating any of it. At its peak SourceForge reported hosting hundreds of thousands of projects and serving millions of users and millions of downloads a day.
SourceForge defined the template for the “forge,” the all-in-one project-hosting site. The pattern it established, hosting plus collaboration tooling in one web service, was the model that later platforms such as Google Code, Bitbucket, and GitHub refined as distributed version control and social workflows took over.