Software Creation Golden Rules...

@Drogon I used a IIGS as my primary computer from 1989 through 1996. I still have it today (and recently I've been using it more… I recently added an ethernet card and a VidHD (HDMI) card, bumped the RAM up to 5 MB, added an ADB-USB adapter so I can use a decent mouse and keyboard, and I have been trying out various modern storage options. (I have a CFFA3000, BMoW Floppy Emu, and an SD2SCSI.) The BASIC in ROM on the GS was the same 8-bit Applesoft found on every Apple II model since the II+. Yes, it runs in 65C02 emulation mode and has no GS-specific features. The Byte Works eventually published GSoft BASIC but that didn't come out until 1998 (!!) so I've never used it. I do own a copy of it though, as I recently bought the full set of Byte Works software. (the Opus ][ collection from https://juiced.gs/store/opus-ii-software/) You can also get a free copy of GSoft from the Byte Works at http://www.byteworks.us/Byte_Works/Morgue.html Most commercial software for the GS was written in assembly language, of course. The first 65C816 compiler was ORCA/M for the Apple //e (for people who replaced their 65C02 processor with a 65C802). When Apple was developing the Apple IIGS they licensed ORCA/M from the Byte Works and paid them to update it for the GS. Apple resold it under the name APW (Apple Programmer's Workshop) while also allowing the Byte Works to continue to sell both the //e and IIGS versions under the name ORCA/M. Apple stopped updating APW after a short while and wrote their own 65C816 assembler to run inside MPW (Macintosh Programmer's Workshop) and encouraged people (including all internal developers at Apple) to write their code on the Mac instead. The Byte Works continued to develop ORCA/M after APW was abandoned and IMHO the ORCA environment is the best development environment on the GS. The Byte Works also published ORCA/C and ORCA/Pascal. (And later ORCA/Modula-2 and ORCA/Integer BASIC, although the latter was mostly just a toy language intended as a tutorial in compiler design (it included the complete ORCA/C source code for ORCA/Integer BASIC). I used ORCA/Pascal for most of the software I wrote in the early 90s. It outputted perfectly acceptable code, at least for the stuff I was writing. (But then I wasn't writing any games or much of anything else that was super performance-sensitive. When necessary I just wrote assembly language subroutines with ORCA/M.) ORCA/C followed the ANSI C89 spec, and has since been updated with partial support for C99. It still gets occasional updates in the GitHub repository: https://github.com/byteworksinc/ORCA-C Apple had their own APW C (completely different from ORCA/C) but it was based on K&R C and I don't think it was used very much. There was supposed to be an APW Pascal but that project got canceled before it produced anything. MPW C could also output 65C816 for the GS but I don't know whether it was K&R like APW C or whether it was a more modern variant of C. I've never used any of the MPW stuff. There were at least two other GS-native development environments that I can remember. The Merlin 16 assembler from Roger Wagner Publishing and TML Pascal (later renamed Complete Pascal). I never used Merlin much (I preferred ORCA) and I've never even seen TML/Complete Pascal (although I'm sure there must be copies floating around on the web somewhere). For cross-development on modern machines (as opposed to ancient 68K Macs that ran MPW) there's Merlin 32, an open-source 65C816 assembler by Brutal Deluxe at https://www.brutaldeluxe.fr/products/crossdevtools/merlin/) and there's Golden Gate (http://golden-gate.ksherlock.com) which allows you to run the ORCA (or APW) compilers under macOS/Windows/Linux/Solaris. Golden Gate is a bit quirky, as it actually runs the original executables inside a 65C816 emulator and maps the GS/OS system calls to native system calls but it works pretty well. Probably only the assemblers would be use useful for writing code for non-GS systems. I'm pretty sure the ORCA libraries that get linked into any ORCA/C, ORCA/Pascal, or ORCA/Modula-2 program rely heavily on the GS toolbox. (I imagine the same is also true of any of the APW/MPW/TML high-level languages.) Plus they output multi-segment OMF executables that depend on the GS's System Loader (basically equivalent to the dynamic linker on a modern operating system) to perform symbol resolution and relocation and to set up a stack and direct page. But with ORCA/M you can write a program that fits into a single segment and use ORCA's MAKEBIN utility to turn it into a memory image suitable for loading at a given memory location. (By default $2000, the address at which ProDOS 8 SYS files load.) Merlin can also generate non-OMF files. Any 65C816 machine that is going to support programs over 64K will probably want to have some kind of similar object format that can load pieces of a program into different banks and fix up cross-bank references. I'd probably just use Apple's OMF format (as it would make it easier to use the existing linkers and other tools intended for the GS) and write a loader for that. A simple OMF loader wouldn't need a full operating system like GS/OS underneath it. Just have some sort of basic memory management routines in the ROM and you could put the loader in ROM too.