ExactImage is a fast C++ image processing library. Unlike ImageMagick, it allows operation in several color spaces and bit depths natively, resulting in much lower memory and computational requirements. Some optimized algorithms operate in 1/20 of the time ImageMagick requires, and displaying large images can be as fast as 1/10 of the time the "display" program takes.
LibRaw is a library for reading RAW files obtained from digital photo cameras (CRW/CR2, NEF, RAF, DNG, and others). LibRaw is based on the source codes of the dcraw utility, though some of the drawbacks of dcraw have been eliminated. The users of the library are provided with an API to be used when writing their software programs.
Ghostscript is a processor for PostScript and PDF files. It can rasterize these files to a wide variety of printers, devices for screen preview, and image file formats. Since applications tend to prepare pages for printing in a high-level format such as PostScript, most Unix users with low-level bitmap printers, such as inkjets, use GhostScript as part of the printing process. In addition, Ghostscript is capable of converting PostScript files, functionality comparable to Adobe Acrobat Distiller, but on the command line. In addition, Ghostscript is used for file import and viewing by a great many other applications, including xv, ImageMagick, gimp, and xdvi. Several GUI wrappers for viewing PostScript and PDF files exist, including GSview, ghostview, gv, ggv, and kghostview. This is far from a comprehensive list.
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.
Virtual MIDI Piano Keyboard is a MIDI event generator and receiver. It doesn't produce any sound by itself, but can be used to drive a MIDI synthesizer (either hardware or software, internal or external). You can use the computer's keyboard or mouse to play MIDI notes. You can use the Virtual MIDI Piano Keyboard to display the played MIDI notes from another instrument or MIDI file player.
Kwave is a 24-bit sound editor that allows simple operations, such as cut, copy, and paste. Some more effect functions with little complexity (Simple Filtering, Delay) are also implemented. More sophisticated analysis functions (spectrograms, sonagrams, pitch determination) are underway or partially done.
Skype uses P2P (peer-to-peer) technology to provide voice- and video-based communication with other Internet users. The technology is extremely advanced, but easy to use. It features excellent sound quality, end-to-end encryption, and automatic negotiation of firewalls or routers. Among major features are SkypeOut and SkypeIn, adding the possibility to make low-cost calls to land line phones and having a fixed number to be able to receive calls from land line phones.