PuTTY - Popular free terminal application. Mostly used as an SSH client.
Seald - Keep your conversations secure, everywhere.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
iTerm2 - A terminal emulator for macOS that does amazing things.
Keybase Chat - End-to-end encrypted chat built into Keybase