Photo Viewers & Browsers

Lightweight image viewers — open a folder of JPEGs / raws fast, page through with arrow keys, rate, rotate, batch-rename. Different from the catalog-shape DAM tools in Photo DAM & Management (those scan, index, and stick around); viewers are stateless and open the file you point at. For raw develop see Photo RAW Editors; for fast culling specifically see Photo Culling & Rating.

Windows (free)

• ★ FastStone Image Viewer — free for personal use, closed source. The Windows default for two decades; full-screen browse, EXIF panel, batch rename / convert / resize, slideshow, raw preview. Reads CR3 / NEF / ARW. Lightweight, fast.
• ★ IrfanView — free for personal use, closed source. The other Windows default; even smaller / faster than FastStone. Tons of plug-ins (raw, RAW, PSD, etc.).
• XnView MP — free for personal, paid for commercial. Cross-platform sibling of XnView Classic; nicer UI. Strong batch tools.
• HoneyView — free; from the Bandizip team. Extremely fast slideshow; minimal feature set.
• ImageGlass — MIT, open source; modern UWP-style Windows viewer; lightweight and active.
• JPEGView — GPL; tiny, fast, single-file Windows viewer; great for old / slow machines.

macOS (built-in + alternatives)

• ★ Preview — built into macOS; opens raws via Apple's RAW pipeline (works for most cameras within ~6 months of release). Star-ratings via Finder tags. Often enough for casual browsing.
• Apple Photos — built-in; library-shape, not folder-shape. Great if you live in iCloud.
• EagleFiler — paid; document-and-image organizer.
• Phototheca — paid; library-shape.
• Lyn — paid; lightweight folder-browser; reads raws.
• Xee — paid; classic Mac image browser.
• qView — open source; cross-platform; minimal.

Linux (free / OSS)

• ★ Geeqie — GPL, GTK; the long-running OSS Linux image browser. Folder tree, EXIF panel, ratings, multi-pane compare. Default on most Linux distros.
• ★ Nomacs — GPL, Qt; cross-platform (Linux/Win/Mac). Modern UI, plugin system, panorama / synchronization view.
• gThumb — GPL, GNOME; integrates with GNOME desktop, basic editing.
• gwenview — GPL, KDE; KDE's default; integrates with digiKam.
• Shotwell — GPL, GNOME; library-shape (less viewer, more mini-DAM).
• feh — GPL CLI / X11 viewer; tiling-WM friendly; the keyboard-shortcut purist's pick.
• sxiv / nsxiv — GPL CLI; tiny, fast, scriptable.

Cross-platform / web

• Lightbox-Gallery type web tools — see Lightbox & Gallery for in-browser display.
• Eagle — paid macOS/Win; popular with designers for moodboard-shape browsing.
• Pictomio, PicView — niche freebies.

Raw preview support

• JPEG preview only — most viewers (Preview, FastStone, IrfanView with plug-in) decode the embedded JPEG inside a raw, not the full sensor data. Fast but cropped to camera-JPEG quality.
• Full raw decode — digiKam, RawTherapee, darktable do real demosaic; slower but accurate. Use a viewer for browsing; switch to a develop app for actual editing.
• XnView MP and Nomacs can do both depending on settings.

Batch operations

• FastStone, IrfanView, XnView MP — all have powerful batch-rename / convert / resize built in.
• ImageMagick / ExifTool from a viewer's "open with" menu — CLI is still king for big batches; see Watermark & Batch.

Pick this if…

• Default free Windows browser: FastStone (full-featured) or IrfanView (lightest).
• Default cross-platform free browser: Nomacs or XnView MP.
• Default Linux: Geeqie (GTK) or Nomacs (Qt).
• macOS, just want to browse: built-in Preview is fine.
• Tiling-WM / keyboard purist on Linux: feh or nsxiv.
• Modern UI on Windows: ImageGlass.