It's a fantastic educational project, as well as a fun way for more experienced programmers to scratch the "low-level coding" itch. I've used older versions of Octo with after-school groups, and I was pleasantly surprised to discover that other educators have made use of it in their own curricula[0].

There's a colorful history to how and why a number of mutual incompatibilities crept into CHIP-8 specs and programs over the decades. In addition to a range of "quirks mode" flags to adapt to differences in behavior, Octo recently gained a tracing linter (Toolbox -> Binary Tools -> Linter Mode) which can flag the use of features which differ between VIP CHIP-8 and SCHIP.

[0]https://www.researchgate.net/publication/338558857_Aplicacio...

Thanks for creating this.

I used to do this thing on my HP48 where I would switch between two GROBs rapidly and the slow screen would give me white, gray, and black. Any of the chip8 emulators support that?

https://github.com/JohnEarnest/Octo/blob/gh-pages/docs/XO-Ch...

To my knowledge, a handful of emulators have attempted to recreate the HP-48's slow display, but I'm not aware of any surviving CHIP8/SCHIP programs that try to take advantage of this behavior to produce grayscale. XO-CHIP bitplanes are indeed somewhat similar to alternating framebuffers, as you describe, from a programming standpoint.

It also now has Vim keybindings, it's a bit hidden in the menu but makes a big difference using it.

Yep! A number of people had asked for a vim mode over the years.

You can also use Octo's assembler from the commandline if you wish, although you will need to pair it with a separate emulator for that workflow. Tom Swan has a high-quality emulator suitable for this purpose, for example[0].

The Octo github page links[1] third-party syntax highlighting modes for a wide variety of external text editors. The Sublime mode is the most actively-maintained; if anyone likes using Vim, Emacs, Atom, or so on, you could help out by sprucing up any that are out of date.

[0] https://github.com/TomSwan/mychip8

[1] https://github.com/JohnEarnest/Octo#links

Looks like a fun side project. In a similar vein, I'd also recommend the Synacor Challenge, which involves a set of gradually expanding challenges around implementing a virtual machine: https://challenge.synacor.com/