There are 4 repositories under appleiigs topic.
A .Net-based Cross-Assembler for Several 8-Bit Microprocessors
An Apple IIgs Emulator and Debugger written in C/C++ for Windows, Linux and macOS
DSKalyzer Apple II disk image management tool
65816 assembly language (various Apple IIgs assemblers) syntax support for TextMate / Sublime Text
Marinetti tcp snooper CDA.
A quick and dirty HTTP server used to mount Apple II disk images on a PC for use with an Apple IIgs using NetDisk.
Convert cc65 libraries and object files to OMF. WTF.
utilities for the Merlin 8/16+ assembler
Kent's Emulated GS with changes to remove status window updates