PuTTY - Popular free terminal application. Mostly used as an SSH client.
TLDR pages - The TLDR pages are a community effort to simplify the beloved man pages with practical examples.
ConEmu - ConEmu-Maximus5 is a full-featured local terminal for Windows devs, admins and users. Get better console window with tabs, splits, Quake style, copy+paste, DosBox and PuTTY integration, and much more.
CheatKeys - View Windows keyboard shortcuts in the current application.
Gnome Terminator - Terminator is one of the most useful and dynamic terminal emulators for Unix based operating systems.
explainshell - Match command-line arguments to their help.