What is SourceForge used for?

SourceForge is used for hosting and downloading open-source software. It provides project pages, file downloads, mirrors and basic dev tools (issue trackers, wikis) for tens of thousands of open-source projects, and it also runs a general business-software directory with reviews.

Historically it was THE home of open source in the 2000s, before GitHub absorbed most active development. Today its main practical uses are: downloading established open-source apps (many older but maintained projects still distribute there), finding mirrors for large binaries, and browsing its software directory.

Worth knowing: during 2013–2016, under previous ownership, SourceForge bundled adware into some installers. That reputation still follows it, though the practice ended after the 2016 acquisition. For active development and newer projects, GitHub/GitLab are where the ecosystem lives now.