TLDR pages - The TLDR pages are a community effort to simplify the beloved man pages with practical examples.
PuTTY - Popular free terminal application. Mostly used as an SSH client.
CheatKeys - View Windows keyboard shortcuts in the current application.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
explainshell - Match command-line arguments to their help.
iTerm2 - A terminal emulator for macOS that does amazing things.