DockLens shows live thumbnails of all an app's windows when you hover its Dock icon. Click a thumbnail to switch, or close, minimize and full-screen windows right from the preview. Windows you closed with the X button (Notion, Slack...) stay listed so one click brings them back, and Spotify / Music get a playback bar. Free, open source (GPLv3), no network access, 0% CPU when idle. macOS 26+.