Thought I'd share this as it's really neat
KnightOS is a third-party Operating System for Texas Instruments z80 calculators. It offers many features over the stock OS, including multitasking and a tree-based filesystem, delivered in a Unix-like environment. KnightOS is written entirely in z80 assembly, with a purpose-built toolchain. Additionally, the KnightOS kernel is standalone, and you can use it as the basis for your own powerful operating systems.
You can download the latest (experimental) version here: http://www.knightos.org/download/
I'm reading HN on hn.premii.com (which uses the Algolia API) and I see both the submission URL and the submission text.
BTW thanks for the awesome work you're doing on HN!