There are countless different RTOS. The most polishing one is Zephyr. FreeRTOS is more like "Scheduler" than a proper OS.
Also am i correctly assume you want an OS that's truly "cross-platform", that can run on every architecture ? Or you just want to "have an app on ESP32 to run on Android" ? Because the latter can be done with proper abstraction layer.
Also am i correctly assume you want an OS that's truly "cross-platform", that can run on every architecture ? Or you just want to "have an app on ESP32 to run on Android" ? Because the latter can be done with proper abstraction layer.