cxmon is an interactive command-driven file manipulation tool inspired by the "Amiga Monitor" by Timo Rossi. It has commands and features similar to a machine code monitor/debugger, but it lacks any functions for running/tracing code. There are, however, built-in PowerPC, 680x0, 80x86, 6502 and Z80 disassemblers and special support for disassembling MacOS code. cxmon is primarily intended for emulation development but it can be used as a generic tool for manipulating and analyzing binary data and machine code, or just as a hex calculator.
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.
SIDPlayer is a replayer program for C64 music (SID tunes), running under BeOS and Unix. You can think of it as being a stripped-down C64 emulator that only emulates the CPU and the sound chip of the C64. SIDPlayer can be used as a stand-alone player or, under BeOS, as a plug-in for CL-Amp and SoundPlay.
TinySID is a very small SID player. Current features include 99% 6510 CPU emulation and fat 6581 SID emulation including filters (which sound different to other players). It has nothing to do with other projects such as SIDPlay, and the 6510/6581 emulation is based on routines by Tammo Hinrichs that have been further developed.
Virtual X68000 is a virtual machine that emulates a Sharp X68000 and optionally its DOS API. It will eventually run application programs for X68000 without any proprietary software including ROM BIOS, but currently lacks many key functions and is still in early development phase. Virtual X68000 is written in C++, and uses templates to implement instruction handlers.