What are some alternatives?
When comparing Keybase for Mobile and Keepsafe Unlisted, you can also consider the following products
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Secret for iMessage - Send secret messages that self-destruct in iMessage.
MyChat - Secure instant messenger for any network
Burner Mail - One-click burner email addresses that you can use when signing up on websites to protect your identity and prevent your personal email address from being sold or spammed.
MagicPad - Free, simple, and private, offline text encryption suite.
Phonebot - Make phone calls from within a Slack channel