What are some alternatives?
When comparing Keybase for Mobile and Feem, you can also consider the following products
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Send Anywhere - Send whatever you want, wherever you want
MyChat - Secure instant messenger for any network
LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
MagicPad - Free, simple, and private, offline text encryption suite.
Ruler - It's a screen ruler for Windows.