Update: 21 November 2016 – I now recommend Riot as the best encrypted messenger. It also makes it easy to share files, but is also decentralized and does not force you to use one specific provider.
It any case, it easily allows people to
- send messages to each other, which can be like instant messages or more like emails
- share (large) files with each other.
Even though that might not replace e-mails completely, Peerio at least features end-to-end encryption and is Free Software under the GPL. Thus, it might be a welcome addition to the suite of encrypted communications tools.
Peerio requires an account on a central server and comes with 1GB of space for free, with more available for payment in the future. It also supports two-factor authentication for increased security.
At the moment, Peerio is only available for Chrome, Windows and Mac, with Android and iOS versions supposedly in planning.
But users of GNU/Linux and Firefox need not despair. If one has Chromium, the free version of Chrome, installed and adds Perio to that browser, one can run it like a regular app (without running Chromium as a browser) under most GNU/Linux variants. Usually Chromium will add it to the system application menu automatically after installing it as an extension.
If you want to try out Peerio, feel free to ask me for an invitation. With an invitation you will get 250MB additional free storage space.