Someone posted this https://webvm.io/alpine.html in another community and it made me think of this post. I’ve never used webvm and I suspect there are many downsides but seemed relevant and the demo seems to be able to run a full desktop environment. You have to find a CAD software that supports Linux though which is a controversial topic at best.

There is also Cascade Studio (Demo). Sadly development has stalled, it was a really cool project.

Probably not at all what OP is looking for though since TinkerCAD is just sketch/primitive type workflow, not like openscad.

The really hilarious thing to me is that the NextPush app (unified push provider that can be run on your nextcloud server) is unsupported by nextcloud talk. But it is supported by a bunch of other competing applications.

This probably won’t help with EA and the like adding kernel-level anti-cheat 6 months after release…

Gatgetbridge (your link) has a breakdown of devices they support https://gadgetbridge.org/gadgets/ . You can click through the vendors to find devices which are both “highly supported” and “no vendor-pair”. Meaning most/all the features work without any reliance on the vendor app.

As for the similarity you are asking about with pixel->GrapheneOS, there are very few watches that can run an alternative open source firmware or operating systems apart from the ones that are already open source, like bangle.js, pinetime, etc. Wearables are even more specialized than phones, they require specialized code designed specifically for them and would likely require pretty extreme effort to reverse-engineer.

I use a pebble 2 HR with gadgetbridge but the watch it self runs the old pebble firmware which gadgetbridge talks to. This is fine for me, but if you are looking for a more modern watch you may have to make some compromises.