Below are all of the hints, ordered by the person that provided the hint.

Chatter?

From: Alabaster Snowball

sudo -l says I can run a command as root. What does it do?

User's Shells

From: Alabaster Snowball

On Linux, a user's shell is determined by the contents of /etc/passwd

Machine Learning

From: Alabaster Snowball

Machine Learning Use Cases for Cyber Security

ed Editor Basics

From: Bushy Evergreen

Ed Is The Standard Text Editor

Deep Blue CLI Posting

From: Bushy Evergreen

Eric Conrad on DeepBlueCLI

Deep Blue CLI on Github

From: Bushy Evergreen

Github page for DeepBlueCLI

MongoDB

From: Holly Evergreen

MongoDB Documentation

Reverse Engineering

From: Holly Evergreen

Reversing Crypto the Easy Way

Iptables

From: Kent Tinseltooth

Iptables

Chrome Dev Tools

From: Kent Tinseltooth

Chrome Dev Tools

Curl Dev Tools

From: Kent Tinseltooth

Curl Dev Tools

Edge Dev Tools

From: Kent Tinseltooth

Edge Dev Tools

Firefox Dev Tools

From: Kent Tinseltooth

Firefox Dev Tools

Lynx Dev Tools

From: Kent Tinseltooth

Lynx Dev Tools

Safari Dev Tools

From: Kent Tinseltooth

Safari Dev Tools

Web App Pen Testing

From: Minty Candycane

Web Apps: A Trailhead

Key Bitting

From: Minty Candycane

Optical Decoding of Keys

Bitting Templates

From: Minty Candycane

Deviant's Key Decoding Templates

Graylog

From: Pepper Minstix

Graylog Docs

Event IDs and Sysmon

From: Pepper Minstix

(Events and Sysmon)

SQL Injection

From: Pepper Minstix

SQL Injection from OWASP

SQLMap Tamper Scripts

From: Pepper Minstix

Sqlmap Tamper Scripts

SANS' PowerShell Cheat Sheet

RITA

From: Sparkle Redberry

RITA's homepage

Linux Path

From: SugarPlum Mary

Green words matter, files must be found, and the terminal's $PATH matters.

Event Query Language

From: SugarPlum Mary

EQL Threat Hunting

Sysmon

From: SugarPlum Mary

Sysmon By Carlos Perez

Frosty Keypad

From: Tangle Coalbox

One digit is repeated once, it's prime, and you can see which keys were used

Jq

From: Wunorse Openslae

Parsing Zeek JSON Logs with JQ

Finding Bad in Web Logs

From: Wunorse Openslae

Do you see any LFI, XSS, Shellshock, or SQLi?