A little list of things I find myself always referring to, or I SHOULD always refer to ;)
Bash
Minimal Safe Bash Script Template
https://github.com/progrium/bashstyle
A Diagram of Linux Filesystem Layout
Better Bash Scripting in 15 Minutes
Datastores
DB Fiddle - Great for playing around with SQL
Jepsen - Analyses of middleware/database products.
Linux
100 Useful Unix Commands by Oliver
http://www.pixelbeat.org/cmdline.html
Computer Science Fundamentals
A Gentle Introduction to Algorithm Complexity Analysis - Big O, etc.
Vim
Source Control
gitqlite - Query git repos as if they were sql databases
Javascript
Basic JavaScript for the Impatient Programmer - This is way out of date as of about 2016... Need a better reference.
Node.js
Node Best Practices (41k stars)
Top 10 Mistakes Node.js Developers Make
Python
Cookie Cutter - For scaffolding new projects, since I don't know what Im doing.
Setting Up Python on MacOS So it doesn't suck - Shameless self reference.
Web
Rendering on the web - Server side vs client side rendering.
Charts.css - Simple CSS framework for visualizations
Regular Expressions
Regex101 - Try, test, explain matching rules, share regex's. Awesome.
Java
Java 8 Feature Tutorial with examples
spring-boot-rest-example - Good starter project for spring boot.
Security
The Beer Drinkers Guide to SAML - A good overview of SAML with easy to understand concepts (even if you don't drink beer)
Security Guide for Developers - Good checklist of considerations
An Illustrated Guide to OAuth and OpenID Connect
Architecture/Design
High Level Overview of Architecture Patterns
The 8 Fallacies of Distributed Systems
Many pressures tend to make programs more complicated (and therefore more expensive and buggy). One such pressure is technical machismo. Programmers are bright people who are (often justly) proud of their ability to handle complexity and juggle abstractions. Often they compete with their peers to see who can build the most intricate and beautiful complexities. Just as often, their ability to design outstrips their ability to implement and debug, and the result is expensive failure.
Functional Programming
So you want to be a functional programmer?
Dev Tools
repl.it - Quick coding samples including standing up a webservice
Productivity Tools
Team Gantt - Simple to use planning tool to get a good idea of the overall scope and timeline of a project. Nothing overly complicated. Way easier and better than something like OmniPlan/MS Project or even Asana.
Mermaid - Great diagramming tool with ability to have text source files
Markmap - JS based mindmaps based on Markdown.
DBDiagram - Make DB diagrams with ascii source in JSON
Cloud
Facts
List of Falsehoods Programmers Believe
The List of Secret Knowledge - Many tools for many different purposes.