Bonus: Session does not demand users' phone number. Also no bundled cryptocurrency.[1]
It seems like Session relies on Oxen's network, so while there is no inherent coin it is blockchain backed.
> Session’s onion routing system, known as onion requests, uses Oxen‘s network of Oxen Service Nodes, which also power the $OXEN cryptocurrency. Check out Oxen.io to find more information on the tech behind Session’s onion routing.
Here is more information about what I meant when I used the term "bundled".
They've given Signal quite the fork.