The last version of the SDK and the GCC-based toolchain were leaked a long time ago, which runs on Windows computers pre-Vista. I'll program in C with Sublime Text, and then run the compiler/toolchain in a VM running Windows XP. The VM can see my source code via a shared folder.
I'm waiting on the mail for a flash cartridge to run ROMs on retail hardware, so for now I use the mupen64plus emulator on Mac OS X, but also a more accurate (but slower) one called CEN64 from time to time. Nintendo 64 emulators are kind of odd; the popular ones don't really "emulate" a game console the way I would have expected.
The short answer seems to be to use either SGI's N64 SDK and a modern toolchain (https://github.com/trhodeos/modern-n64sdk) or libdragon (https://dragonminded.com/n64dev/libdragon/). The latter comes at the cost of not having built-in support for 3D (but it seems like there's enough there to take a DIY approach) and also being incompatible with most emulators (which "cheat" a bit by intercepting calls to the original libultra instead of directly emulating all the hardware). One could also run SGI's original compilers/toolchain, whether on a Linux system (using qemu-irix, which is what the folks over at https://github.com/n64decomp have been doing) or on a Windows 98 VM.
I'm waiting on the mail for a flash cartridge to run ROMs on retail hardware, so for now I use the mupen64plus emulator on Mac OS X, but also a more accurate (but slower) one called CEN64 from time to time. Nintendo 64 emulators are kind of odd; the popular ones don't really "emulate" a game console the way I would have expected.
Sometimes I post pictures of my progress on Twitter if you're interested: https://twitter.com/danielsavface/status/1258896460604555264