PuTTY - Popular free terminal application. Mostly used as an SSH client.
Firezone - Firezone is a remote access platform that’s painless to deploy, easy to manage, and built on WireGuard® to be blazing fast. Best of all it's self-hosted and open-source.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
Viscosity - Viscosity is a VPN client for Mac OS X and Windows.
iTerm2 - A terminal emulator for macOS that does amazing things.
Tunnelblick - free software for OpenVPN on OS X and macOS