If you’re interested in the concept behind Tox, I’d recommend taking a look at Jami. Tox’s development has been sporadic at best and I wouldn’t trust it to be a viable solution long-term. Jami runs with the same concept but has multi-device support and is backed by/part of the GNU project so it probably has more staying power. That being said, it’s still (like Tox) not very user friendly at this point.