My opinionated 2¢ on why e-mails will live while many an "e-mail killer" dies mourned by no one.
E-mail is just better way of doing snail-mail, a technology that we had since we first invented writing. One could say that our whole civilization is built on such communication, as one could not conduct business, make a war or govern a country without mail. E-mails is just the same, only faster, and it shares all the benefits with the snail-mail medium. Interestingly, many of those benefits are also shared by... phone.
Why snail-mail, e-mail and phone calls do better than others and will outlast random fads is visible if you look at the structure of the medium. The main features those three forms have that various "e-mail killers" don't are:
- ubiquitous - you can reach anyone...
- distributed and federated - ...anywhere, without caring about whether they subscribe to the same service as you.
The last thing is important. When I send you a snail-mail, I don't know or care how the post office works in your country. When I send you an e-mail, I likely don't know (and again, I don't care) if you pay for your mail server and to whom. When I call you, again, I don't know or care who provides you cellular service. I don't even know what kind of device you use to receive that call.
No single entity owns snail mail, e-mail or the phone network.
On the other hand, with Facebook Messenger you can talk only to Facebook users on Facebook platform. With Asana, I can only talk to other Asana users.
The reasons those services die quickly (when was the last time you ICQd someone? MSNd? or 'd?), and the reasons I STRONGLY WISH THEM TO DIE A QUICK DEATH for are greed and hubris. I go to Asana web-page (I don't mean to single them out, apply this to any other similar service) and I can see that idea, "we will replace e-mail, everyone will use our service and we will rule over in-company communication!", floating in the air. No, this will not happen. There will always be people who won't use your service because they don't like your UI or like a competitor more. But what you're trying to do is to throw away freedom of collaboration and interoperability to earn a quick buck. This is damaging to communications, damaging to society, damaging to humanity, and fortunately will disappear quickly into oblivion, like countless other similar startups.
Want to create an "e-mail killer"? Apply some humility. Accept that you will not be The One Gateway to Human Communication; it would be bad for everyone (yourself included) to become one. Just aim for a federated protocol, awesome UI and play nice with others. Sure, success will not be yours only; many others will profit in the same space as you. But embrace that. Wanting to keep everything for yourself is just greed.