Mastering the art of lurking
in the the wikipedia article it seems to use multiple kernels (either a rtos type kernel for iot and wearable devices or the linux kernel + aosp layer for phones, tablets, etc…) seems that in the new next version they will no longer use the linux kernel but their own kernel instead and move away from android entirely (i got that last bit from this article)
vorta is also a nice front-end for borg
matrix? but that is more of a discord or telegram alternative, session and tox also look interesting for chatting