feh is a fast, lightweight image viewer that uses imlib2. It is command line-driven and supports multiple images through slideshows, thumbnail browsing or multiple windows, and montages or index prints using TrueType fonts to display file information. Advanced features include fast dynamic zooming, progressive loading, loading via HTTP (with reload support for watching webcams), recursive file opening (slideshow of a directory hierarchy), and mouse wheel and keyboard control.
Gifsicle is a powerful command-line program for manipulating GIF image files. It has good support for transparency and colormap manipulation, simple image transformations (cropping, flipping), and creating, deconstructing, and editing GIF animations. It can also optimize GIF animations for space. Also included is a GIF animation viewer and a program that checks whether two GIFs look the same.
Gwave is a waveform viewer. Its purpose is for viewing analog data, such as the output from Spice-like simulations. Gwave can read binary or ascii files written by HSpice from transient, AC, or Sweep analyses, "raw" files written by Spice2, Spice3, or ngspice, and transient analysis files from the CAzM simulator. It can also read a generic tabular ASCII format suitable for use with ACS or homegrown tools. It supports multiple "panels" (graticlules) with multiple variables displayed in each. Two vertical-bar cursors are available for time-difference measurements. Multiple files can be loaded, for comparing the results of several simulations.