BEYE (Binary EYE) is a portable advanced file viewer with a built-in editor for binary, hexadecimal, and disassembler modes. It contains a highlighting Java/AVR/i86-AMD64/ARM-XScale/PPC64 disassembler, full preview of MZ, NE, PE, LE, LX, DOS.SYS, NLM, ELF, a.out, arch, coff32, PharLap, and rdoff executable formats, a code guider, and many other features.
BRL-CAD is a powerful constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing support for rendering and geometric analysis, path-tracing for realistic image synthesis, network distributed framebuffer support, and image and signal-processing tools.
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.
PLIB is a set of libraries to write games and other realtime interactive applications that are 100% portable across a wide range of hardware and operating systems. It's used by Majik3D, FlightGear, and others, and includes libraries for GUI widgets, sound replay, geometry, scene graph, joystick, and fonts/text.
IIViewer is an application for X, and optionally for the Linux framebuffer device. It allows you to display pictures in a directory as thumbnail images. Selected images can then be displayed at full size. It reads BMP, GIF, and JPEG images (even without additional libraries), but it is also able to use libjpeg, libtiff, and libpng.
GImageView is a GTK+ based image viewer. It supports tabbed browsing, thumbnail table views, directory tree views, drag and drop, reading the thumbnail cache of other famous image viewers, and a flexible user interface. It also support movies using the Xine library and MPlayer, and supports images in compressed archive formats like tar.gz, zip, and lha.