I think you can remove "quietly" as is implies something sinister. This is a good thing. They are just reusing code they had internally to better an open source product. Am I wrong?
Historically, Microsoft had an explicit strategy of infiltrating and subverting open standards in order to bring them under their control. I believe that Microsoft are now deeply committed to being a reliable and trustworthy open source contributor, but I understand why other people might be more sceptical.
I don't get what the big deal is about this, am I missing something here? To me it looks like it's just a repo Microsoft forked from react-native.
The repo has only 9 stars and they haven't even changed the README yet. It's not like it's a big open source Microsoft project they're now sinisterly adding Office code to. And even then, the commit title directly mentions Office.
I gave some narrative regarding the 'big deal' in the original thread, and OP shamelessly reposted it just two hours after, so you're missing that ¯\_(ツ)_/¯
Check the 0.51-macos branch if you missed it; it's got ~350 changed files specifically to support macOS.
HN title lengths are very restrictive, so perhaps it was unclear, but what I was trying to say was that this repo is likely receiving merges of the very same codebase that Microsoft is using to build their RN Mac apps. This is the first indication of which fork they're using for it (and it's surprisingly not derived from the fork that has 14k+ stars!).
Slightly off-topic: I wish they'd started the merge from Office 2010 instead of current versions where they've removed essential features like a real dark mode and slimmer to-do bar. Every Outlook release since 2010 has been worse than the last for power users and those with low-res screens or light sensitivity. Outlook 2010 was as good as it needed to be.
Not Electron involved at all. The point of RN is that it is native; no overhead of running headless Chromium. The fact that Microsoft are putting their weight behind it means great things for RN, desktop, and macOS. They say they've finished rewriting most of their core apps with RN; this is the first indication of the codebase they likely used to target macOS. It's come out of nowhere, too: there's a same-named repo with 14k+ stars, for comparison.
Actually it looks like what may have happened is Microsoft is using React Native in their Office apps (to some extent) and with this project are trying to open source it.
They've revealed that they're using RN for all their main products now, but never explained how they were targeting macOS. This is the repo they must have been using; and surprisingly, it's unrelated to the repo of the same name that has 14k+ GitHub stars.
What's brilliant too is that they are indeed open-sourcing it.