https://keybase.io is hard to describe. It started as a place for publishing someone’s public keys if you wanted to send someone an encrypted message or file.
More recently it added a file system, with private and public folders. The private folders are encrypted with user-generated keys that are not held by the keybase servers, so the service cannot read the files, even if they have a sense of how much space the files occupy, and possibly the toplevel folder names.
There is an end-to-end encrypted chat function once you find the person with whom you wish to chat.
Quora tries to explain https://www.quora.com/What-is-Keybase-in-laymans-terms . If you get to the end of that article, the only thing that’s clear is that “it’s complicated”.
A year ago, keybase started to use the blockchain underneath bitcoin to store the keys for file sharing. How cool is that. That part of the blockchain holding the keys, is immutable – exactly which keys and how they are updated (?) is still sorting out in my poor head.
If you sign up for an account today, in February 2017, you get a free 10 gigabyte account for file storage in the keybase filesystem, with the private files encrypted with your own private keys. If you choose to share your files privately, it appears that keybase will encrypt the files end-to-end; that is the only party or parties that will be able to read the files will be the ones you have identified on the directory on keybase.
Keybase shell (installed with the application) allows you to create your own 4096 bit GPG encryption keys. Following the directions (!) actually helps. Or you can bring your own keys if you wish.
Keybase has a presence on the TOR / onion network: http://fncuwbiisyh6ak3i.onion
The applications are only available on Windows, Mac, and Linux platforms. There are currently (Feb 2017) no mobile apps.
This is going to get some getting used to.
Find me on keybase.io by my handle: djilpmh — and see what we can do. Please be patient with response time, I’m doing this in spare time.