Google Keep

Google Keep is a minimalist note-taking service for quick capture of thoughts, lists, and voice memos. It uses labels for organization and integrates tightly with Google Docs and Calendar. It's best for transient notes, shopping lists, and reminders rather than building a knowledge base. It's completely free with a Google account.

It ranks as the top choice for ultra-fast, frictionless capture within the Google ecosystem, serving as a useful 'inbox' for ideas before they are processed into a more structured system.