What started a short list became quite a big description, more details inside the post.
prestissimo - composer parallel install plugin. Speedup package install.
Postgres EXPLAIN Visualizer - designed to make EXPLAIN output easier to grok. It creates a graphical representation of the plan.
Mongotron - Open Source, cross platform MongoDB management tool, built using Electron and Angular JS.
favico.js - JS lib to make use of your favicon with badges, images or videos
You Dont Need jQuery. Side-by-side examples, how to replace jQuery calls by native JS selectors etc. Mostly we don't need jQuery in modern browsers and GUI frameworks.