Acorn

An A4xx-series emulator for UNIX/Linux, RISC OS and Windows. Source code is available, as are ports for Mac OS X, GP2X and Amiga OS4.

Open source BBC Micro Models B/B+ and Master 128 for Windows. Links to ports for diverse platforms including Mac OS, UNIX/Linux, PlayStation Portable, and Pocket PC.

Horizon (formerly MacBeebEm) was one of the first emulators available for Macintosh.

A collection of Electron games in Universal Emulator Format.

An open source emulator for Mac OS X and Windows. Older versions for DOS and Linux are also available, as is the source code.