Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
Or SailfishOS! Has Android layer where apps can run seamlessly (without some hardware stuff support, like fingerprint etc.).
Want to mention that on GNU/Linux we also have Waydroid that provides Android app support :)
I know about that, but from my experience nothing really compares to the ease of use of the SFOS AlienDalvik. Though something may have changed since I last checked (1.5 years ago).
I mostly wrote it for other readers.
Also used both, I would say they are similar. But Waydroid can't forward notifications to the main OS as in Sailfish. Sad that AlienDalvik is not FOSS :(