7-Zip is a free, open-source file archiver for Windows, written and maintained by Igor Pavlov since 1999. It opens and creates archives in its own 7z format, which compresses very well, and in ZIP, TAR and GZIP, and it can unpack many more formats, including RAR and ISO files. Most people meet it the same way: a ZIP from a colleague is fine with Windows, but something else needs a proper archiver.

It is a utility rather than an app you open every day. Once it is on your PC, right-click any archive in File Explorer and the 7-Zip menu offers Extract Here or Extract to a named folder, and right-click any files to add them to a new archive. The main window looks dated, but it is fast and does not nag, and its Test command checks an archive for errors before you rely on it, which is worth doing with backups. For sending large folders, the 7z format with a password gives you AES-256 encryption, which is handy for contracts or invoicing files you want to protect in transit.

What to check before relying on it: 7-Zip has no official store listing, so make sure you are on the developer's own website, 7-zip.org, before you install anything; copies on other sites have been bundled with unwanted software in the past. If your PC has an ARM processor, pick the matching edition on the developer's site. Corporate PCs may block it, in which case Windows' built-in ZIP support covers the basics. The facts below come from the winget and Chocolatey package registries, which track the developer's releases.