http://cht.sh/ - I use this a lot. It outputs a short summary of common commands for many cli tools. You can curl to it https://cht.sh/grep for example or install their cli client
doc () { curl "https://cheat.sh/$1" | less }
Cheat Sheet Help : https://cht.sh/:help
Cheat Sheet List of topics : https://cht.sh/:list
Being able to use curl as a client as well is so powerful as well. Whenever you are using ssh on some vps you can still get cheatsheets for all your commands.