Google Drive
Google's cloud storage + file collaboration. Launched April 2012 (after Google Docs existed since 2006). Drives Google Workspace (formerly G Suite). 15 GB free.
Client: web, desktop ("Drive for desktop"), mobile. File types include Google-native (Docs, Sheets, Slides, Forms) + uploaded files. Version history per file. Collaborative editing via Operational Transformation (originally) → migrated to more modern architecture. Drive integrates with Gmail (attachments → Drive at >25MB). Competitors: Dropbox, OneDrive, iCloud Drive, Box.