vega/vega-lite

D3.js (d3/d3) is an open-source JavaScript library, described in its own README as free to use, for turning data into visuals directly in the browser. Rather than offering a fixed menu of chart types, it binds data straight to SVG, Canvas, or HTML elements using a low-level approach built around existing web standards. The repository carries an ISC license and is available on GitHub.

Helm is the standard way to package and deploy applications to Kubernetes clusters — think apt for containers. It wraps your YAML manifests into Charts, which bundle a Chart.yaml metadata file with Kubernetes templates that Helm renders and pushes directly to the cluster API. The release management side is what separates it from raw kubectl apply: you can upgrade, roll back, and track exactly what changed between versions, which matters enormously when you're debugging a production incident. The v4 mainline is where active development lives, while v3 is in extended support until late 2026, so most shops are either already on v4 or have a runway to migrate. Installation is trivial — a single binary you drop on your PATH, available through every package manager worth mentioning. The ecosystem is enormous: Artifact Hub surfaces thousands of community-maintained Charts for nearly every piece of infrastructure you might need. The catch is that writing good Charts from scratch requires learning the template syntax and Helm's values injection system, which has a real learning curve, and debugging a bad render is not fun when you just wanted to understand why your Deployment isn't picking up the right image tag.

The interactive graphing library for Python :sparkles:

The System Design Primer is donnemartin's GitHub collection for learning large-scale system design and preparing for the system design interview. It combines topic explainers, a four-step interview framework, worked case studies, and Anki flashcards into one repository.