There's WebOS and Tizen. I haven't used either, but heard Tizen's codebase is abysmal. WebOS is by LG, Tizen is by Samsung.
MeeGo was a combination of Intel's Moblin and Nokia's Maemo. I'm not sure what became of Intel's efforts after MeeGo. Sailfish is the successor of Maemo/MeeGo whereas Mer is an open source mobile Linux OS which Sailfish uses as base. Both utilise libhybris [1] for Android compatibility layer. Backwards compatibility = important; no apps / ecosystem = no users, and that curve is very steep.
Another interesting effort I saw the other day is actually from Google. An effort to easily build an app which is easily ported to Android and iOS. That might directly benefit Android and Google most, but indirectly it could benefit libhybris users. I'm unsure how good Sailfish 3's Android compatibility is these days. It used to be Android 4.4 compatibility for a long time.
MeeGo was a combination of Intel's Moblin and Nokia's Maemo. I'm not sure what became of Intel's efforts after MeeGo. Sailfish is the successor of Maemo/MeeGo whereas Mer is an open source mobile Linux OS which Sailfish uses as base. Both utilise libhybris [1] for Android compatibility layer. Backwards compatibility = important; no apps / ecosystem = no users, and that curve is very steep.
Another interesting effort I saw the other day is actually from Google. An effort to easily build an app which is easily ported to Android and iOS. That might directly benefit Android and Google most, but indirectly it could benefit libhybris users. I'm unsure how good Sailfish 3's Android compatibility is these days. It used to be Android 4.4 compatibility for a long time.
[1] https://en.wikipedia.org/wiki/Hybris_(software)