Ubuntu Touch is still around, see [0]. That said, with continued funding by Canonical, they like would have progressed differently (likely more).

Firefox OS and webOS are still around under different names, which are Capyloon [1] and LuneOS respectively [2].

[0]: https://ubuntu-touch.io/

[1]: https://capyloon.org/

[2]: https://webos-ports.org/wiki/Main_Page

Interesting, I had thought KaiOS was the last remnant of FFOS.

I wonder which of these projects is most active at this time.

Firefox OS was built from a lot of Android internals.

WebOS!