Cross-platform (Chrome web-apps don't count), Federated, Distributed, to name a few. The reason email is so entrenched is probably because of these reasons enti

Cross-platform (Chrome web-apps don't count), Federated, Distributed, to name a few. The reason email is so entrenched is probably because of these reasons entirely. Being able to send a message from any provider to any provider certainly helped spread adoption easily.