A little list of things I find myself always referring to, or I SHOULD always refer to ;)
DB Fiddle - Great for playing around with SQL
Jepsen - Analyses of middleware/database products.
Computer Science Fundamentals
A Gentle Introduction to Algorithm Complexity Analysis - Big O, etc.
gitqlite - Query git repos as if they were sql databases
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.
Rendering on the web - Server side vs client side rendering.
Regex101 - Try, test, explain matching rules, share regex's. Awesome.
spring-boot-rest-example - Good starter project for spring boot.
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
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.
repl.it - Quick coding samples including standing up a webservice
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
The List of Secret Knowledge - Many tools for many different purposes.