Evernote is a tool that allows users to store notes, documents, photos, and more across all of their devices. It can be used to archive communications, create to-do lists, store personal information, and act as an "external brain" to remember everything. Users can add content by typing notes, emailing to their Evernote account, dragging and dropping files, or using the mobile camera. The robust search functionality allows users to find content by keyword, tag, notebook, or attributes like location and date. Premium subscriptions provide additional storage and features like sharing notebooks and annotating PDFs.