The iCloud Photos Downloader is a command-line tool that allows users to download all their iCloud photos. The tool is available for Linux, Windows, and macOS, and can be installed via various package managers or run as an executable. It provides features such as automatic de-duplication of photos, support for Live Photos and RAW images, and optimization for incremental runs. The tool is designed to solve the issue of downloading an entire iCloud library at once, which is not possible through official Apple methods.