SIMH is a historical computer simulation system. It consists of simulators for approximately 20 different computers, all written around a common user interface package and set of supporting libraries. SIMH can be used to simulate any computer system for which sufficient detail is available, but the focus to date has been on simulating computer systems of historic interest.
KStella is a KDE frontend to the Atari 2600 emulator, Stella. It currently supports the display of snapshots, labels, manuals, the configuration of individual game settings and of course, the ability to play games with just a click of the mouse. All these features are fully customizable to allow maximum flexibility.
GNS3 is a graphical network simulator that allows you to design complex network topologies. You may run simulations or configure devices ranging from simple workstations to powerful Cisco routers. It is based on Dynamips, an IOS emulator which allows users to run IOS binary images from Cisco Systems and Pemu, a PIXOS emulator to emulate PIX firewalls.
Z88Transfer is a transfer utility written with Python and PyGTK that allows a Linux machine to send and receive files from Z88 computers (created in 1987 by Sir Clive Sinclair in his last computer company, Cambridge Computers). Z88transfer supports IMP-EXPORT, EAZYLINK, and PCLINK-II protocols, and can convert automagically between Abiword/RTF format and PipeDream, Z88's native format.