I'm a big supporter of open-source software. I co-maintain an emulator for arcade games using the Intel 8080 microprocessor, named LASER (Little Arcade System Emulator Releases) with ss_teven. The emulator was based, with permission, on SinVader by Mike Green (the creator of EmuDX, the arcade emulator with graphic and sound enhancements... the EmuDX enhancements are now supported in Raine).
I also have contributed to the codebase, and I am one of the wiki maintainers, of ScummVM.