Frodo is a free, portable C64 emulator. It focuses on the exact reproduction of graphical effects possible on the C64, and comes in three "flavors" (Frodo, Frodo PC, and Frodo SC) with increasingly higher quality of emulation, but at the cost of higher processing power requirements. Frodo has been ported to a number of systems, including handheld computers. The Unix version can use either SDL, X11, or SVGAlib to display the graphics.
The Free Unix Spectrum Emulator (Fuse) is an emulator of the 1980s home computer and various clones. It emulates the Spectrum 16K, 48K, 128K, +2, +2A, +3, +3e, and SE, the Timex TC2048 and TC2068, the Pentagon, and the Scorpion. Almost all the common Spectrum emulator file formats are supported, including .rzx input recordings, .tzx tape images, and .szx and .z80 snapshots.
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.
MDK (MIX Development Kit) provides tools for developing and executing, in a MIX virtual machine, MIXAL programs. The MIX is Donald Knuth's mythical computer, described in the first volume of The Art of Computer Programming, which is programmed using MIXAL, the MIX assembly language. MDK includes a MIXAL assembler (mixasm), a MIX virtual machine (mixvm) with a command line interface, a Guile-based virtual machine (mixguile), a GTK+ based GUI (gmixvm), and a mixvm-Emacs interface (mixvm.el). MDK utilities are extensible using Scheme.
GRUB for DOS is a rebuild of the GNU GRUB boot manager for DOS, and can be run under real mode DOS. It also has many new features. It can be booted through BOOT.INI of Windows (grldr) and kexec of Linux (grub.exe). It can directly boot NTLDR (WindowsNT/2K/XP), IO.SYS (Windows9x/Me) and KERNEL.SYS (FreeDOS). The disk emulation feature is another enhancement over GNU GRUB, and can be used to run legacy DOS/Windows9x systems with floppy or hard disk images.
GSport is an Apple IIgs emulator based on Kent Dickey's excellent KEGS emulator. It features updated support for the Uthernet Ethernet board, as well as virtual printer support. Code from several KEGS variants over the years was merged together to form this codebase. GSport's name comes from the merging of "GS" (as in the Apple IIgs) and portability - in the programming sense - since it can be built and run on many different computer platforms.