nomacs is a free image viewer for windows and linux systems. nomacs is small, fast and able to handle the most common image formats. A more detailed documentation can be found here. Furthermore it provides additional features as listened below.

Image Viewing

• supports the most common image formats including RAW (see table below)
• fast thumbnail preview (Screenshot)
• display exif information (Screenshot)
• framless view (Screenshot)
• change transparency of windows (Screenshot)
• display overview while zooming (Screenshot)
• display histogram
• file filtering/searching
• improved anti-aliasing (cool for displaying highly textured images)
• hide menubar and toolbar
• slideshow
  • image information (e.g. date created)
  • play/pause with user defined time interval
  • adjustable background color

Image Editing

• crop images (Screenshot)
• resize images (Screenshot)
• pseudo color function (Screenshot)
• color adjustments (brightness/contrast/saturation …)
• rotate images
• drag and drop images
• automatically save screenshots
• delete/rename images
• set wallpaper (windows only)

Viewer Synchronization

• synchronize multiple instances (Screenshot) (Howto)
  • synchronized zooming
  • synchronized panning
  • synchronized next/previous file
  • overlay of two or more instances (with changing opacity)
  • arrange synchronized instances
• synchronize multiple instances in the LAN (Howto)
  • synchronized zooming
  • synchronized panning
  • images can be sent over LAN connection